His more famous exploits include drinking his own urine, eating grotesque grubs and sheltering inside a dead animal's carcass.

However, there's more to Bear Grylls than meets the eye. After years of adventure, both in and out of the TV spotlight, more injuries than he cares to remember (including a broken back which shattered his military career), conquering Everest and toughening up celebrities and ordinary folk in extreme environments, Grylls reckons he's not as brave as he used to be.

"I get more and more full of fear as life goes on," says the son of late Conservative politician Sir Michael Grylls, whose wife Sally still lives in the family home at Winterborne Zelston, near Wimborne.

"I wish it wasn't like that. I struggle with jumping out of planes after breaking my back, I struggle with groups of people that I don't know. I struggle with self-belief a lot of the time, and that battle becomes a harder one to win as the years go on.

"I wish I could tell you you're looking at the invincible hero, but that just wouldn't be truthful."

Today, we're here to discuss a safer strand of his career, his latest novel Burning Angels, the second in a trilogy featuring ex-SAS hero Will Jaeger who, in this episode, Jaeger tackles germ warfare, a jungle island overrun by rabid primates, conservation and poaching, illegal arms dealing and a hunt for his lost wife and son.

"The whole premise of all three books is inspired by what my grandfather (Ted Grylls) was trying to do," he says.

Brigadier Ted Grylls was the commanding officer of Britain's elite T-Force unit, tasked with capturing Nazi scientists after the D-Day landings and spiriting them away to the West to stop their knowledge falling into the hands of the Soviets.

The novel is an action-packed page-turner, but not totally written by Eton-educated ex-SAS soldier and Chief Scout Grylls himself - Damien Lewis, former-war-reporter-turned-thriller-writer, is co-author.

It's amazing he's been able to fit the book into his packed schedule, although having his ITV show Mission Survive axed after the second series freed up some time.

He's just commissioned another series for ITV, based on the one-on-one Hollywood guests for Running Wild [Barack Obama famously joined him on an adventure for that one].

But family - Grylls has three sons with wife of 16 years, Shara - has altered the limits as to what he'll personally take on, too.

Shara has lived with Grylls' penchant for dangerous challenges ever since they met.

"I was still in the Army when we first got together. I initially built a life through all the expeditions and then through the TV stuff, and she quietly trusts me to make good decisions and always come back in one piece."

He says he's become adept at slotting back into family life - on their houseboat in London and their island in North Wales - when he returns from his adventures but, at 42, Grylls says he has to work much harder these days to keep fit.

"The thing is, I don't want to reach the end of my life with a perfectly preserved body. I want to arrive covered in scars, screaming, 'Yahoo! I've arrived!'

"I should have died a zillion times but I'm still alive and I'm lucky to be a survivor. I hope to still be doing it when I'm 65."

:: Burning Angels by Bear Grylls is published by Orion, priced £18.99. Available now