Standing on a sloping limestone ledge, the spray from the swell below falls far short of the bottom of my wetsuit. Time it right, land on the top of a wave and I can cut 4ft off my jump. Time it wrong and the fall is farther, with less sea to protect me when I break the water, 40ft below, at 35 mph.

I lean forward, past the point of no return, then a kick pushes me out over deeper water. Count the seconds - one, two - before impact, my final expletive cut short by a great gulp of salty green seawater.

Then, grinning and relieved, I swim to the rocks. Timing is, again, important. The waves can help or hinder, as they push and pull me on and off the cliff: to begin my climb, ready to jump again.

There is an accepted history of tombstoning. At the turn of the millennium, thrill-seeking teenagers began to travel to the coast, leaping off sea cliffs and piers from increasingly dizzying heights. Ignoring the warnings of their parents, the coastguard, newspapers - and even paralysed former tombstoners - they risked death or serious injury. All for a brief adrenaline rush.

But that was not the whole story. What the cautionary tales always ignored - what parents neglected to mention and newspapers didn't understand - is the most important fact of all. Tombstoning is a lot of fun.

Of course, the conventional history of tombstoning is also wrong for more fundamental reasons: not least that the activity has always existed.

Dan Brown and his friend Ben Norton are perhaps the closest thing that the UK has to a central tombstoning body, although really they just got lucky with a web domain. “We realised tombstoning.com was available and decided to buy it,” Dan says. “Initially, we wanted people to send in tips about good spots, but we're not really that sort of community. So we simply say what we do and give advice on keeping it safe.”

The Royal Society for the Prevention of Accidents (Rospa), initially wary about the sport, has contacted tombstoning.com about ways to make it less dangerous. Rospa recorded five tombstoning-related deaths last summer, and three people have already been seriously injured this year. At some piers police have been given powers to stop people jumping. But Peter Cornall, Rospa's head of water and leisure, explains that the society is not interested in banning the sport - even if it could. “What we want to do is tell people how to minimise the risks: to check the depth; make sure they can get out once they are in; and realise that even though it is deep enough one day, the tides may be a lot lower another day,” he says. “Even people who go tombstoning don't jump in thinking that they are going to get hurt - they still want to be safe.”

Most weekends in the summer Dan and his girlfriend Natalie join Ben and his wife Emily and drive to Stair Hole in Lulworth Cove, Dorset, to scramble on the rocks, relax in the bay and jump off the cliffs. They agree to introduce me to the sport, which they only occasionally refer to as tombstoning, but are wary of how they will be represented. “I think the name is more of a hindrance,” Dan explains. “You meet people - old guys who live along the coast - and they say, ‘I've been doing this for 30 years - when did it start getting called tombstoning?' It's such a moody word.”

Stair Hole is an improbable geological formation of the kind that makes geography teachers happy. A continuation of the coastal cliff, it juts out as a tall limestone peninsula, cutting off most of a small bay. To get to the open sea, you have to go either around it, or through two archways formed by erosion. It is a playground for tombstoning.

We begin with the lower jumps, pulling ourselves up the cliff to a series of ledges. A small crowd watch from the shore as we go higher - until we are 10ft above the largest arch, the Stair Hole itself, contemplating a drop that involves jumping out to avoid hitting the top of the arch.

A bellow, a leap, and I am clear. I am fearless, intrepid, bold.

Later, the Times camerawoman - shooting a video for timesonline - shows me the footage. Standing on the ledge, I tense up, as if about to jump, then retreat to lean against the cliff. This happens three times before, with a look of terror, I scream like a girl and overbalance off the edge.

“I'm so pleased you could get to do all these jumps,” Dan says afterwards, bobbing in the water beneath the arch - his head occasionally submerged when a large wave breaks. “It took us weeks to get to this stage - we worked through the lower ledges, testing the depth, getting gradually higher. If you don't touch the bottom on a 15ft jump, then you know you will be safe at 20ft and so on. In most cases your legs will absorb the difference. That's why we never go head-first - there's a lot more room for flexibility in your legs than your neck.” Above him, Ben cartwheels off a 15ft jump - falling backwards into the sea.

Their hobby might seem reckless, but then so is rock climbing, paragliding - or any extreme sport. And as with all extreme sports preparation is essential. “Every jump we have done, we have spent time snorkelling around the bottom - figuring out how to get to it, what's in the water, working out where is safe, where is not safe,” Ben says. “When people get injured it is because there is not enough water. It's such a simple thing: check the tides and check the depth. Of course, you get three cans of Stella in you and that's the last thing on your list.”

That is often the issue.

When reading stories about tombstoning tragedies, skip the first paragraph - where the victim talks about how his life has been ruined for ever. Skip the second paragraph, where he urges others to learn from his example. Skim past the description of how he was rescued, how he narrowly avoided death and how he is still grimly positive.

Then, more often than not, the victim will grudgingly concede that before throwing himself off a pier without bothering to look down first, he'd had a few drinks. That isn't tombstoning.

But such activities do have a pedigree - before being called tombstoning, they were known as “tragically injuring yourself after acting like a drunken idiot”.

Not all injuries are as a result of drinking, but they do all have one feature in common. By definition, the water can't have been deep enough. This is an aspect that Dan believes the media wilfully ignore. “BBC Radio Five convinced me to come on for an interview - they said they wanted to chat about tombstoning,” he says. “It turned out that all they really wanted to do was to get me on air, confront me with a guy who had been paralysed and for us to get into a slanging match. They would ask a question and he would say how horrific tombstoning was then they would say to me: ‘What do you think?'

“What was I meant to say? If he had checked the water, he wouldn't be paralysed. I can't call him an idiot, he's a tetraplegic. You wouldn't jump from 30ft into concrete. So why would you jump 30ft into a foot of water?” Thirty feet is the highest jump on the sheltered side of Stair Hole. With the bay forming a natural amphitheatre, the imagined taunting of daytrippers - not to mention an expectant Times photographer - had impelled me to throw myself off. But these are the nursery jumps, the green runs of tombstoning.

Moving to the seaward face, accessible by a steep climb over the top, the jumps are higher, the water choppier and there is no crowd.

We conquer the second-highest, and decide to leave the highest for another day - the sea has dropped too far. Resting afterwards on a wide ledge, the sun sets behind a distant Portland Bill - refracting orange in the spray above our cliff's base. It would be romantic were it not for the half pint of sea water drizzling out from my sinuses. On hitting the waves, water funnels inside your nose at 15m a second: odd sprays would surprise me for another 24 hours - exiting unannounced whenever I cocked my head.

We have one final jump, before the tides make it unsafe. But I'm already planning my next trip. It's been more exhilarating than I had imagined.

“Really, we just do this because we love the water,” Dan says. “We like every aspect of it. It's as much fun snorkelling around the bottom, checking out there's enough depth, as it is jumping.”

Emily, Ben's wife, adds: “It's the adrenaline, the fear, the buzz, the relief when it's over - then you can go back to your job and remember that there's more to life than work.”

SAFETY TIPS FOR TOMBSTONING

Check the depth: This cannot be emphasised enough. Every major tombstoning accident has been due to there not being enough water. So snorkel around the site, look out for obstacles such as boulders and, if possible, start with lower jumps.

Be aware of changes: What is safe one day may not be on another day. This is not just because of tides - which can be checked on easytide.co.uk - but also because of shifting sandbars, or more treacherous weather.

Make sure you can get out: Most people drown within reach of land. Even if the jump is safe, an exit point is just as important. A cliff that is easy to climb in good weather may be impossible in a swell.

Don't drink: Safety organisations advise against drinking and swimming - it is certainly dangerous to drink and tombstone.

Use local knowledge: With so many factors involved, it is always easier to speak to people who understand the tides, the cliffs and what is going on under the waves.