Police have revealed they believe all four London bombers died in the blasts, following a series of raids and an arrest. The BBC News website is covering events as they unfold (all times in BST):
1730 West Yorkshire Chief Constable Colin Cramphorn urges the public to be "alert but not alarmed". Extra police are on the streets and they are there to protect all communities in West Yorkshire, he says.
1725 A third controlled explosion has been carried out on a suspect car at Luton railway station, police say.
1713 Asst Comm Hayman appeals for people to stay calm and says the explosions are the work of "extremists and criminals". He asks that no community is smeared as a result.
1712 The home addresses of three of the four suspects have been searched. Material found at one of the six addresses raided has caused police concern. One man was arrested in West Yorkshire and has been brought to London for questioning.
1709 CCTV footage shows all four of the men arrived in London by train on the morning of Thursday 7 July. Personal documents link them to the scenes of some of the explosions, Mr Clark says. One suspect had been reported missing by his family.
1708 Peter Clark, head of the Met's anti-terrorist branch says they were alerted quite early to the activities of four men, three from the West Yorkshire area.
1707 Asst Comm Andy Hayman says police have followed up more than 2,000 calls to an anti-terrorist helpline. They have also studied 2,500 CCTV tapes.
1705 Met Police hold a press briefing on the day's developments.
1650 Security sources confirm they believe all four bombers are dead. They suspect the three on the Tube were suicide bombers but are keeping an open mind on whether the bomber who died in the bus bomb meant to kill himself, the BBC's Margaret Gilmore says.
1638 Counter-terrorist officers tell the BBC they believe all four of the bomb suspects are British born. They suspect more than one died in the blasts.
1630 Police confirm a second controlled explosion is to be carried out on a car in Luton.
1604 Counter-terrorist officials reveal they have made arrests in West Yorkshire in connection with the London bombings.
1555 A controlled explosion is carried out on a suspect car in Luton.
1549 Police confirm they believe the bomber of the No 30 bus died in the blast in Tavistock Square.
1548 Police say they are searching the car, which is parked in a multi-storey car park in Luton.
1512 Luton railway station is evacuated and cordoned off as police recover a vehicle suspected of links to Thursday's bombings.
1506 Met Police announce they are carrying out an operation at Luton station.
1425 Police in Leeds say they are searching for explosives at the property in Burley. They carried out the controlled explosion to gain entry to the unoccupied house.
1347 Sir Ian describes the operation in West Yorkshire as "significant" in the investigation of the London bombings.
1328 A controlled explosion is carried out by army bomb disposal officers at an address in Alexandra Road, Burley. It was one of the six houses raided.
1130 Up to 600 people are evacuated from homes and shops in the Burley area of Leeds.
1000 Police cordon off a second neighbouring Beeston street and search a property between the two roads. Two properties in Dewsbury are also searched.
0920 Police are reported to have cordoned off a street in Beeston, Leeds.
0900 Scotland Yard commissioner Sir Ian Blair announces the operation in West Yorkshire - the first linked directly to the bombings.
0630 Anti-terrorism officers launch a series of raids on six houses in the Leeds area.