Kenyan Martin Lel sprinted home to win a second London Marathon crown from Morrocan debutant Abderrahim Goumri.
Haile Gebrselassie dramatically pulled out after 19 miles with stitch.
China's Zhou Chunxiu won the London Marathon at her very first attempt ahead of Gete Wami with Briton Mara Yamachui an excellent sixth.
There was a British double in the wheelchair race as David Weir defended his title and Shelly Woods claimed the women's crown for the first time.
ALL THE ACTION AS IT HAPPENS (ALL TIMES BST)
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1200: Just before the chimes of Big Ben strike noon, Britain's Dan Robinson comes home in ninth to round off a good day for the British contingent.
"I am an unemployed chef, just texting to say Come on Gordon Ramsay and I was wondering if gordon would give me a job!"
1155: The men's race reaches a thrilling conclusion as the quartet of Lel, Limo, Gharib and Abderrahim Goumri round the final stretch on The Mall. The legs of Lel have it in the end as he sprints to the finish line in 2:07.42 to add to his 2005 crown. The Kenyan pips marathon debutant Goumri ahead of defending champion Limo.
"Best wishes to Haile Gebreselassie and I hope that he is all right."
Lesley by email
1145: The men's race is coming into the last mile as they run along The Mall, down the Thames, and there are still six men in contention. Gharib tries to break up the pack but he is sucked back in by Lel and Limo.
"Best wishes to Jane Pithie from all at Severn Trent Water on her third marathon and in her 50th year, running for the Warwickshire & Northamptonshire Air Ambulance. We are so proud of you."
Fraser by email
1130: The men have just gone through the 22-mile mark with American Ryan Hall right up there at the front of the field ahead of Martin Lel, Limo and Tergat. Looks like this one could go right down to the wire.
Gebrselassie tells the BBC Sport the reason he pulled out was because of stitch: "I'm not injured but I had stitch and I could not breathe. I don't know what is going on."
1120: China's Zhou Chunxiu wins the London Marathon at her first attempt in 2:20.38. The 28-year-old storms down The Mall to finish convincingly ahead of Gete Wami, also making her London debut. The consistent Constantina Tomescu-Dita runs a brilliant tactical race to claim third.
Britain's Mara Yamachui tunes up for the World Championships in Osaka later this summer with an impressive sixth-place finish. Liz Yelling also pulls a personal best of 2:30.44 out of the bag for a top-10 finish.
1118: There is drama in the men's race as Gebrselassie pulls out in the Canary Wharf area with 18-19 miles run. The Ethiopian distance legend, bends down and holds his chest but still manages a wave and a smile to the crowds. After describing his ninth-place finish in 2006 as his worst result ever - things have got even worse in 2007.
1115: Blackpool race Shelly Woods wins the women's wheelchair race in 1:32.14 to win a double for Great Britain.
"Watching the results scroll through from Washington DC and thinking of my nephews Paul and Ben Draper who are running for Christie's Hospital in Manchester. Paul has just finished treatment for brain cancer - running this was his statement of the power of life and of his indomitable spirit. Wish I could have been there."
From Tig by email
1112: Zhou unleashes a 5:09 minute mile as she streaks further away from Wami as they come in alongside the Thames. The Chinese athlete is setting her sights on the Beijing Olympics - where she could pose a threat to Paula Radcliffe's medal hopes.
1110: The main pack continues to pound away with the pace makers doing a decent job up to the 17-mile mark. At the front, American Ryan Hall is a surprise contender while Olympic champion Stefano Baldini and Khalid Khannouchi are drifting away from the bunch.
"Come on Andrew the Geordie Dancer, from all at Thorn Close"
"Today is the day that made all those cold and wet winter nights pounding out the miles on your own all worth it. Well done everybody."
Brian via email
1101: Kiplagat has fallen away from the front of the women's leading pack leaving Zhou of China to open up a gap ahead of Berlin Marathon winner Wami.
"That is a gap that could be very, very significant indeed. Zhou came here with question marks over her ability to win big city marathons but she is answering that now."
BBC commentator Steve Cram
1100: Still no major breaks in the elite men's race after 14 miles with Ramaala, Lel and Gebrselassie lined up at the front of the pack.
1056: The first winner of the 2007 London Marathon is Britain's David Weir in the wheelchair event. The 27-year-old successfully defended his own title ahead of Paralympic champion Kurt Fearnely. The duo came into The Mall together but Weir injected the pace to cross the line in 1:30.51.
"Good luck Nick Butlin. Running for Snowdon Trust. One foot in front of the other, love all the family.xxx"
1053: In the women's wheelchair race, Britain's Shelley Woods is far and away ahead of the rest of the field and looks on course to break the course record too. In the men's race, it is still a game of cat and mouse between Weir and Fearnley.
1048: The mass of fun runners are in high spirits as they round the Cutty Sark and weave their way through Greenwich.
1045: The conditions are beginning to take their toll on some of the front runners. The experienced Adere has fallen back to eighth after being "reduced to a jog," in the words of BBC summariser Brendan Foster. Benita Johnson is struggling too but Briton Yamachui is going really well and has moved up to sixth.
"Good luck Kim Sanders from all your work colleagues and friends at the Haynes International Motor Museum. Our very own museum marathon man."
1035: The elite men have been running for 53 minutes now and all the talent is still bunched together. Limo has made some sort of mini-break a few metres ahead of the pack but the drama is sure to be played out later on.
"The men are on schedule for a finish time of two hours and seven minutes."
Five Live commentator Mike Costello
1035: At the front Kiplagat seems to be injecting a little bit of pace and the three leading athletes slip into single file.
"Kiplagat knows there is an awful lot of experience behind her."
BBC commenator Steve Cram
"A big good luck to my Uncle Peter who's running for St Clares Hospice and my Uncle Clive who is running for Special Wheelchairs For Kids."
Lucy via email
1027: Weir and Fearnley are neck-and-neck in the men's wheelchair race so an exciting finish is in store there. They are averaging about 19/20 miles per hour.
"Jane wanted some rain but her big smile has brought out the sunshine, keep on running girl."
From Crewe via text
1026: The women's race has come down to three athletes - Kiplagat, wearing huge sunglasses, leads the field with Zhou, running with her arms loose, in second ahead of Wami in third. They have run through 16 miles in 1:25.30.
1017: Limo heads up the men's field as he rounds the Cutty Sark at the 6-mile mark with Martin Lel, Hendrik Ramaala, Jaouad Gharib and Haile Gebrselassie all close. Dan Robinson rounds the ship, which is under restoration - and he is Britain's leading hope now after Jon Brown pulled out this morning with illness.
1011: The women have remarkably reached the halfway point already and Kiplagat leads the pack after going through in 1:09.58 ahead of Adere and Zhou. The London Marathon is acting as the trials for the Worlds for the British runners and Yamauchi and Liz Yelling are going well in eighth and ninth.
"Good luck to club physio Jen Bowman running for Guys Hospital."From Warrington Wizards RLFC via text
"Come on Ken! You're a champ, see you at the 25-mile mark. Rock on!"
From Anita, by email
1000: The men picked up the pace by 20 seconds in the third mile with Limo leading the field at this very early stage.
"That third mile has just shaken them up a little bit."
BBC commentator Steve Cram
In the women's race, Kiplagat looks composed and comfortable at the front as they come through the 12-mile mark. She is being tracked by Zhou Chunxiu and Adere.
1000: The fun runners are still squeezing through the gates of Greenwich Park and getting on their way.
Costume alert: The old faithful Rhino, Superman and two men wheeling a golf cart.
"Good luck from the Netherlands expecially to Lornah Kiplagat and Gordon Ramsay who has a lot of fans here! Go go go!!"
Jacqueline from the Netherlands via email
0955: The elite men have gone through the first two miles and the world-class contenders are bunched together. The pace is pretty slow, they came through the first miles in 4:56 and 4:59.
0952: A trio of wheelchair racers have broken away, defending champion Weir, Fearnley and Roger Puigbo.
0950: The elite women are approaching the 10-mile mark and there are still half a dozen runners in contention. Kiplagat, making her London debut, is still clipping the heels of the pacemakers ahead of Benita Johnson and Adere. Yamauchi has been cut adrift and is having to run her own race but is still going well.
"Good luck Erica Marks. Running her first marathon at 42. She is running in aid of Whizz Kidz. We think she's crazy but we're so proud of her."
From her family via text
0945: All smiles at the start line as defending champion Felix Limo, the marathon world record holder Paul Tergat and distance legend Haile Gebrselassie are introduced to the crowd ahead of the elite men's race.
Ronan Keating shouts out "Come on" as he lowers his flag and the elite men charge off - with streams of club runners behind them.
0941: Just four minutes to go now for the mass of runners, who are snaking their way round from the start line in Blackheath. The advice is to take on as much water, as often as possible - because it could get pretty sticky later on.
0937: David Weir has been making little breakaway moves in the wheelchair race to try and break up the field, but, just like in the women's race, the main contenders are all still in the mix.
"Good luck to Garioch lad Brian Ross running his first marathon," love Mum x
Via text to 81111
0930: Back at the front of the race, the two pace makers are clipping the front runners along at a pace of 5:22 per mile. The towering figures of Lornah Kiplagat and Berhane Adere are leading the pack as they round the Cutty Sark in Greenwich.
Mara Yamauchi is the leading British runner in the race but she is 48 seconds adrift of the main contenders.
"Good luck Clare and Matt, who will come first the chicken or the egg?"The Village Idiots via email
0925: Britain's defending champion David Weir is out to set another course record in the wheelchair race but he faces a tough challenge from Paralympic champion Australian Kurt Fearnley, who is making his London Marathon debut.
0915: We are through the first three miles of the women's race now and Lornah Kiplagat has nosed into the lead, going through in 16 minutes and 24 seconds. The Dutch runner seems to be pushing the pace on but, at this early stage, the runners remain bunched in two packs.
0905: So the women have officially got the 27th London Marathon under way, and the next race to start will be the wheelchair racers at 0925. An exciting elite men's race will get under way at 0945 - the same time as the mass of runners will embark on their own journeys from the red and green starts.
0900: It is estimated 35,500 runners have made their way to the start line but the elite women go first and former Boyzone singer, Ronan Keating, and Mary Peters press the buzzer to set them on their way.
"They are perhaps the warmest conditions we've had for the London Marathon, and the women have an advantage here starting 45 minutes ahead of the men."
BBC commentator Steve Cram
0850: The elite women are making their way to the start as they prepare to begin their trek over the 26.2-mile course. It will be a warm race, with temperatures expected to reach 23C, and it looks like it will be played out under blue skies.
An absolutely top-quality men's field contests the London Marathon, amongst them is the world record holder Paul Tergat, Olympic champion Stefano Baldini and world champion Jaouad Gharib.
Kenyan Felix Limo out-sprinted compatriot Martin Lel in the final 200m to capture the 2006 title, and they will both be right in the mix again.
But the spotlight shines most brightly on Ethiopian great Haile Gebrselassie, double Olympic 10,000m champion and winner of four successive world titles over the distance.
Gebreselassie, 34, does have form in the marathon after deciding to give up running shorter races last year. His personal best of 2:05.56, set when he won in Berlin in 2006, is the fifth fastest of all time.
The question remains, however, whether one of the sport's most popular figures can win in London. He finished third on his debut in 2002 and ninth last year, in what he called "the worst race of my career".
To help us all keep track of just who is coming round the bend, the leading contenders are all wearing colour-coded kits: Tergat is in all-yellow, Baldini goes in gold, Gebreselassie wears a red top and white shorts, Limo dons red shirt and blue shorts and Gharib wears all-grey.
The London Marathon serves as the trials for British athletes with one eye on going to Osaka for this summer's World Championships, and that is what the likes of Dan Robinson and Huw Lobb have on their minds.
Paula Radcliffe is working her way back to her very best form after giving birth to baby daughter Isla in January, but the London Marathon comes too soon for the world record holder.
So with Britain's best watching from Colorado, well maybe, and defending champion Deena Kastor opting out to compete in Boston last week, where she finished fifth, the women's race could be pretty open too.
The one to watch here is 28-year-old Chinese athlete Zhou Chunxiu, who says she is only using this race as a stepping-stone to the Beijing Olympics in 2008, when Radcliffe will certainly have her eye on gold.
Zhou is the Asian Games champion and is the fastest woman in the field with a personal best of 2:19.51. She also became the first woman in 2005 to run four sub-2:30 marathons in a year.
Ethiopia have strong claims for the crown with Berhane Adere, who won in Chicago last year, and Gete Wami, who is making her debut in London.
Lornah Kiplagat and Benita Johnson are also in the mix while Britain's challenge is led by Mara Yamauchi, who is the second fastest Briton with a time of 2:25.13. Kathy Butler and Liz Yelling also fly the flag.
Britain's David Weir set a course record on one hour, 29 minutes and 48 seconds on his way to winning last year and is pretty confident about defending his title in record-breaking style again.
But Weir, 27, is up against a tough, tough rival in Paralympic champion Australian Kurt Fearnley. Fearnley is chasing his seventh straight marathon win but is making his debut in London.
Former Paralympic wheelchair basketball player and BBC Television personality Ade Adepitan is also taking part for charity and has been picking up tips from Weir, so that will be worth watching.
In the women's race, Italian Francesca Porcellato is chasing an unprecedented fifth title but Britain's Shelley Woods will chase her hard.