Motorbike racer and television presenter Guy Martin has announced he is attempting to set a new world record by cycling around the British coast in 20 days.

Martin, from Grimsby, set off on his latest challenge on Sunday morning and is hoping to be home by Christmas Day.

The 4,802-mile pedal-powered ride is the latest world record attempt by the 35-year-old TT star, who has set speed records in a variety of human and engine-powered vehicles.

In a video message filmed before he began the challenge, Martin said: "We've got a big job on. Record's stood since 1984, I'm going to try and break it."

He added: "I'm setting off to try to break the record of pedalling around the circumference of England, Scotland and Wales. That's what I'm doing.

"The record, as it stands, is 22 days, I'm going to try and do it in less than that. The record's stood since 1984. No-one's broken it, no-one's come near it, so, it all starts here.

"It's further than you'd think. It's 4,802 miles, that's what the official record distance is, 4,802."

Martin continued: "I am nervous. It's a bloody long way on a push bike in not a lot of time. I'm going to try to do it in 20 days. Obviously I want to do it in anything less than 22 - 21.06 is the official record.

"If I finish any time before 5 o'clock on Christmas morning, then I've broke the record, any time before then.

"I've got to do 250 miles a day, every day. If I do 250 miles a day, I think it will take me 18 and a half days. We'll see. It's a big job. Biggest job yet. But I like a challenge."

Truck mechanic Martin has already set world records for fastest speed on a gravity-powered snow sled, fastest speed in a soap box and highest speed on a wall of death.

Earlier this year, he attempted to break the two-wheeled world land speed record in a purpose-built 400mph Triumph motorcycle, but was thwarted by conditions on the course at the Bonneville Salt Flats in Utah.

Martin said he would return to motorbikes next year.

He said: "We'll be back next year motorbiking. In what form, we don't know yet. Got a few miles to do before then."

The world record for fastest ride around the coast of Great Britain is held by Nick Sanders, who completed the distance in 22 days in 1984.