David Cameron saved me from a shoal of hideous giant jellyfish

TV historian Andrew Roberts told yesterday of the day the Tory leader heroically plunged into the sea off the south coast of France to save him from a school of huge, stinging jellyfish.

It was a moment, Roberts says, that showed Cameron's 'great physical as well as moral courage'.

And while the story has often been told among the Conservative leader's inner circle, it has never been fully aired publicly - until now. The fact that the party's conference begins today may, of course, be purely coincidental.

Cameron was 29 and on holiday in Miramar, in the South of France, with his wife Samantha when they joined friends for a boat trip.

Also on board the vessel, which belonged to writer Robert Hardman, was journalist Petronella Wyatt, Andrew Roberts and his girlfriend, now his ex-wife. It was a hot day in August 1995 and the group, Roberts says, had just enjoyed 'a very jolly lunch'.

"I can't remember what we ate now,' he said, 'but it was the South of France so of course wine had been taken."

Roberts, then 33, insisted on swimming 100 yards from the boat to reach two local landmarks known as Les Deux Freres - 80ft tall, red, volcanic monoliths standing side by side and dominating the horizon.

He said: "For some reason at that time I had a thing about jumping off very tall rocks into the sea. I don't do it now that I have children. But at that time, if I saw tall rocks in the water, I had an indescribable urge to leap off them. "At first everything went rather well. It didn't take me long to climb up them, and I stood at the top, waving and showing off. The water beneath was very deep, so I knew I wasn't about to break my leg, or anything worse, when I jumped off."

Roberts then plunged into the blue waters, emerging to wave triumphant at his friends on the boat. But suddenly he felt a 'hideous, lacerating sting' on his upper left arm - and when he looked around him he began to panic.

"The sea was swarming with a horrible, menacing school of large jellyfish, one of which had stung me,' he said. "It was frightening. They were transparent with a green tinge and had very long tentacles. There must have been 40 or 50 of them, so large that you would have struggled to squash one into a bucket.

"I yelped and squealed and waved desperately at the boat, but because of the rocks Robert couldn't bring it in to reach me.

"I knew that if I had to swim blind through the jellyfish, many of which were hiding under the surface, I would be repeatedly and badly stung. Things weren't looking good."

It was then that Roberts saw David Cameron leaping off the boat. "I realised he was coming to my rescue. He had goggles and had grabbed a spare pair for me. I still don't think it's something most people would have done.

"He swam within about 20 feet of me, through some of the jellyfish, to perform an Olympian throw. It was pretty impressive - it's not easy to throw any distance or with any accuracy when you're in water. He played cricket at Eton, I think, so that no doubt helped.

"I grabbed the goggles and then I could see where the jellyfish were, so I could navigate through them. Dave was doing the same."

Once clear of the danger, Roberts and his rescuer hurriedly swam back to the boat. "I was thinking of all the stories I'd heard about jellyfish and how some of them are deadly,' he said. "Back on the boat, I think I had a beer.

"It seems funny now, but at the time I was terrified. The welt on my arm stung for about two days. If Dave hadn't rescued me and I'd been forced to swim through the jellyfish, I would probably have been hospitalised. It would certainly have ruined my holiday.

"I told him he was a hero, and I was serious. But he quite typically brushed it off. He's always downplayed it whenever I've mentioned it."

The anecdote is likely to feature in a fringe speech Roberts is giving at the Conservative conference in Bournemouth tomorrow.

"I'll be talking about what advice past great Tory leaders, such as Disraeli and Churchill, would give to Cameron if they were alive today,' he said. "I've witnessed first-hand Dave Cameron's physical courage, but he has great moral courage, too. Both are prerequisites for a great leader."