Coasteering may sound like something you try to do with a supertanker (usually with a spectacular lack of success) but it is in fact part of a new generation of hybrid outdoor activities which blend bits of conventional sports for the greatest possible thrill.

Gone are the days when you could just hoof it for hours across moorland and relax at the end of the day with a job well done. Now the holy grail of physical exertion is exhilaration and achievement - confront your fears and feel the buzz. Besides, Blue Peter has just tried it and liked it and there is no greater accolade for an outdoor activity.

But what is it exactly? Coasteering is what you get if you mix a little rock climbing with a pinch of cliff jumping, throw in some pounding Atlantic swells for good measure and enjoy. Technically it is a cliffside scramble. You traverse around the coast at sea level, climbing, scrambling, swimming and leaping into and across churning watery gullies to get from A to B. But it is much more than the sum of its parts, as anyone who has tried it will testify.

The sport was “invented” at Twr-y-Felin Outdoor Centre in Pembrokeshire about 10 years ago. Several instructors realised that an activity that they had been doing informally for years could be incorporated into the centre’s programme. However it did require some degree of tailoring so that all ages and fitness abilities could enjoy it. I remember being invited to take part in an “exploratory” coasteer around Ramsey Island off the St David’s Peninsula. Although we were all pretty fit, we only got about halfway before cold, fatigue and pending darkness forced us to give up. Not the sort of thing for a family group on their summer holidays.

Most children living near the coast will have tried a variation of coasteering - usually to their parent’s consternation. The great advantage of joining an organised coasteering group is that you minimise the risk and double the excitement - instructors know all the most thrilling places to explore, without getting hurt.

For anyone who has only seen the spectacular cliffs of the Pembrokeshire coastline from above, it’s a reasonable question to ask why anyone would want to clamber down them and then scramble a mile or two along their base - after all, there’s an excellent coastal path that follows the same route and is a far less strenuous undertaking. But as with so many outdoor activities, if you have to ask why, it’s already too late. Time to search out your Radio Times and a cosy pair of slippers.

Coasteering begins at the top of the cliffs of St Non’s Bay. Here you get handed a wetsuit, helmet and buoyancy aid (you provide your own trainers). It is at this point that most people’s nerves begin to wobble. As you scramble down the cliff face the surging waves of the Atlantic loom uncomfortably closer. The best time to coasteer is in summer when the water is so clear you can see the kelp and boulders 20 feet down and although it may look alarming, the bigger the swell, the more fun you’ll have.

The coastal scramble is always pitched at a level appropriate for the particular group. No one should be struggling but there will be challenging sections where there’s a reasonably good chance you’ll fall. This may seem suicidal in the extreme but with coasteering falling is part of the package.

There is something vaguely surreal about floating in the ocean as the swell lifts you like a cork and the cliff face you were clinging to minutes before moves up and down like a stage curtain. This same swell will try to suck you off the rocks if you climb too low so there is always the challenge of finding the right “line” on any traverse. The instructors at Twr-y-Felin usually devise their routes so that there is invariably some point where no one but Spiderman could get any further without getting soaked, so in you go.

These leaps of faith - and they are huge - are always one of the most exhilarating aspects of the coasteering adventure. Just how much do you trust your instructor? How deep is that water, really? But even timid members of a group are emboldened after falling 15 feet through empty space to land unharmed with a massive splash. After that, it is very much a case of once is never enough.

Coasteering is now Twr-y-Felin’s most popular summer activity. Director Andy Middleton says: “It’s quite surprising how quickly it’s taken off but on the other hand, I can see the attraction, especially for children. After all, I grew up around here, enjoying my own unsupervised coasteering expeditions as a child 30 years ago, and I know that my own kids get just as much of a kick out of it - the only difference is that they can do it in a far safer environment.”

It has also proved particularly popular for school groups. Mandy Watts who accompanied a group of pupils from Ashford Park primary school in Middlesex says: “It appeals to their sense of adventure and also gives them an opportunity to face their fears in a safe environment.” Other teachers claim it can challenge pupils in a variety of ways and promote a team spirit at the same time.

Twr-y-Felin Outdoor Centre, 1 High Street, St David’s, Pembrokeshire SA62 6SA. Booking office: 01437 720391. The cost for half a day’s coasteering is pound;25 each and includes helmet, wetsuit and buoyancy device. Discounts may be available for groups visiting out of season. As the sport is so popular, try to book well in advance.