Jamie has started his 150 mile journey, joined by wife Sophie - waving a giant green flag at the starting line - and a crowd of cheering supporters.

Speaking to Radio 1's Charlie Hedges:

"He's been so nervous. He just doesn't wanna let anyone down, but he's gonna be amazing."

Jamie Laing
Radio 1's Ultra Marathon Man

You’re going to see the good, the bad and the ugly with me this week. I’m not going to hide anything.

Radio 1 Breakfast's Greg James had some words of advice for Jamie before he set off.

Back in 2018, Greg took on a big challenge for Sport Relief, scaling all of the UK's tallest mountains - and cycling between them in treacherous, snowy conditions!

"My only advice is let the adventure happen to you," Greg tells Jamie. "You can’t predict how your body will feel, how your brain will feel. But there will be some magical moments. The challenges I’ve done are the best memories I’ve got. All good things are hard to do."

Greg reveals the challenge felt so daunting, his wife Bella Mackie proposed to him the day before it started. "Bella was so scared for my challenge that she proposed the day before. So that was a nice thing to have in my head while I was doing it."

"So Greg," Jamie replies, "are you going to propose… to me?"

Image source, BBC / Comic Relief

Before setting off on the first of five ultra marathons, Jamie Laing joined Greg James in the Radio 1 studio, and he's a bag of nerves.

"It feels like the first day of school. I packed my bag, ate a banana and kissed my wife."

Jamie's wife, Sophie Habboo, is here to see him start his challenge. "She’s more nervous than me. She can hardly talk."

When Jamie said yes to the Ultra Marathon Man task, he hadn't run more than a 5k. "But you know what… I’ve run some 10ks. I’ve run a 25k. It was a bit sore! But you know what, I have no idea what this is going to feel like, because my body hasn’t done this before. That’s the scary part."

Jamie's put together a special Pace Setter playlist of all his favourite tunes.

These songs have soundtracked his training for the past few weeks, so they're probably whirring round his head as he takes on the UK's pavements.

Listen below or via BBC Sounds, where you can also subscribe to future Pace Setter mixes.

Radio 1's Jamie Laing is attempting to run five Ultra Marathons in five days - between London and Salford - all to raise money for Red Nose Day.

The challenge starts today (17 March), as our beloved presenter takes the first of many hundreds of thousands of steps. We're expecting him to start just after 8am.

He tells us he hadn't run a 5k prior to training for this challenge. So it will be an almighty test of endurance and strong will. He'll need all the help of the Radio 1 listeners to get him to the finish line.

Click the player at the top of this page to listen live, or follow this page for every update as we track his progress.

Image source, BBC / Comic Relief