Mayo started his show at 0900 GMT on Thursday - and hasn't stopped broadcasting since. He plans to stop at 2200 on Friday, by which time Comic Relief's telethon on BBC One will be in full swing, featuring a host of celebrities led by Lenny Henry, Griff Rhys Jones and Steve Wright.

The last Red Nose Day, in 1997, raised more than £27m, for the vulnerable and disadvantaged in Africa and the UK. This year's theme is record-breaking - and the team aim to break a record every 45 minutes during the TV broadcast.

Strict rules on record attempt

Starting his marathon broadcast

According to a spokeswoman for Radio 1, Mayo's record attempt is being strictly audited.

"There has to be two witnesses in the studio at all times, and the whole show has to be videoed and sent back to the Guinness Book of Records for checking," she said.

Each record played has to be no less than two minutes long, and no more than six minutes long, while there are conditions laid down as to the amount of news and other items that can be introduced.

The event is being supported by record companies, who are donated £100 for each hour to Comic Relief to have their songs played by Mayo. Listeners have also been eager to chip in.

"They've been sending him loads of things to see him through the 37 hours, including lots of energy drinks. And there's no way he's going to be on his own, as the regular DJs will be coming in during their own slots and there'll always be people in the studio to keep him company," the spokeswoman added.

Record-breaking TV show

Mariella Frostrup, Davina McCall, Emma Freud and Geri Halliwell (clockwise) launch the appeal

Mayo can also be watched during his stint via a camera on the Radio 1 Website.

The main Comic Relief TV show comes live from BBC Television Centre in London and the National Exhibition Centre in Birmingham, where Griff Rhys Jones and Steve Wright will be trying to break the record for the most people ever gunged on TV.

Other events bring together Hollywood stars and British celebrities, as well as personalities from the BBC as well as its commercial competitors.

They include a one-off episode of The Vicar of Dibley starring Johnny Depp and the Duchess of York, Victoria Wood stars in a spoof Hetty Wainthrop Investigates special with stars from ITV's Coronation Street. A Doctor Who special will be also be unveiled - featuring Blackadder star Rowan Atkinson as the legendary time-traveller.

TFI on the BBC

A Ginger production: Chris Evans and Geri Halliwell

Meanwhile, Chris Evans brings TFI Friday from Channel 4 to the BBC for a one-hour Comic Relief special. Evans has promised his Ginger Media Group will match every pound raised during the hour he is on air, and has challenged other companies to do the same.

Men Behaving Badly returns for a 10-minute special, while Have I Got Buzzcocks All Over sees host Angus Deayton referee Phill Jupitus, Jo Brand and Meatloaf taking on Nick Hancock, Phil Tufnell and ITN newscaster Carol Barnes in a special news, sport and music quiz.

Other celebrities appearing include Elton John, David Bowie, Woody Allen, Matt Damon, John Cleese, Whitney Houston and U2 singer Bono.

Geri Halliwell talks about her trip to Uganda

There will also be reports on how Comic Relief money is helping the needy - including former Spice Girl Geri Halliwell's trip to Uganda to visit a literacy camp for women.

"When I got there I just started crying. The way these women welcomed me was just fantastic," she recalled.

"They knew I was from the West to help them with this project where they educate women to read and write. We might take it for granted, but 50% of people in Uganda cannot read and write, and most of those are women. It was fantastic how it changed their lives. "

Simon Mayo's The Longest Radio Show In The World... Ever! continues on BBC Radio 1 until 2200 on Friday.