Eighteen metres below the surface, on the sandy floor of the Red Sea, 15-year-old Kris Demester is standing very still. Nosing at his wet suit is a huge moray eel, fully two metres long and thicker than a man’s thigh.

Morays possess an impressive set of teeth and an unpredictable temperament and can, if roused, attack. It was a tense moment for Kris and his fellow divers from Haydon School in Pinner.

“We didn’t know whether he was coming to say hello, or going to bite someone’s leg off. And things look 25 per cent bigger when you’re down there,” the divers admitted later. However, this one is more interested in what the group might have in their pockets.

The trip has been organised by Haydon’s science teacher, Ian Brereton, who is an experienced diver. The school is one of the first customers of Scuba for Schools, a specialist dive-travel company run by diver Dave Perry.

The Red Sea offers some of the best diving in the world. The water here is warm, the visibility excellent and the range of marine life simply staggering. In these waters you can find turtle, shark, the elusive manta rays, and all manner of brilliantly-coloured and peculiar fish. There are also many wrecks including that of the Second World War cargo ship the Thistlegorm, with its consignment of motorbikes, aeroplanes and wellington boots still on board.

Eilat in Israel is already well established as a tourist destination but Egypt is a much cheaper option. Resorts there have sprung up at Sharm el Sheikh on the Sinai peninsular and at Hurghada on the Egyptian coast to cater for the ever-growing diving market. The Haydon group is to complete a course run by the Professional Association of Diving Instructors (PADI) in Hurghada.

After a five-hour flight our first aerial glimpse of Hurghada does not look promising: it is a landscape of rocky desolation, with no roads, signs of habitation, or life. Luckily the town is not so sparse. As a resort it didn’t exist 10 years ago, but now its coast is lined with fabulous hotel complexes.

Day one and the group gathers at a dive centre where the initial training will take place in swimming pools and classrooms. Diving is a demanding sport and survival can depend on your ability to remember decompression requirements and elementary first aid.

One of the first lessons, however, is an introduction to diving kit, of which there is an enormous amount: tank, regulator, depth gauge, pressure gauge, weight belt, mask, fins, wet suit, buoyancy-control device, snorkel, boots...

There’s also a steep learning curve to putting it all on. For this you need a helping hand from your buddy or diving partner. He or she is not just there to help strap the tank on your back, but to run through safety checks with you and help you if you get into difficulties under the water. The entire sport is based on the fundamental premise that safety is best maintained by diving in pairs, with each individual having responsibility for the other’s safety.

The tank containing the air supply is extremely heavy. Someone standing upright will have to fight hard not to topple over backwards. So everyone struggles down to the beach leaning forward and walking very slowly and carefully.

After three days of drills in the swimming pool, theory classes and shallow dives close to the shore, the group is ready to make its first open water dive.

While we are waiting for our boat to take us out to the reef, there’s a commotion and a crowd gathers round a local fisherman who has caught several tuna. After a struggle he brings them to the bank. They’re each just over a metre long - small for tuna, but the biggest fish some of our group have ever seen on the end of a line. We are to have one for lunch.

The mountain of gear is finally loaded on to the purpose-built dive boat and we make our way across the Red Sea to Carless Reef. A horseshoe of dive boats is there already and there are divers bobbing about everywhere, either surfacing or preparing to descend.

Below the surface there is a coral outcrop and a wide wall dropping down to the sea bottom. The current here is fierce and our group has a tough swim against it, so that they can drift dive back to the boat.

Each dive lasts around 30 minutes and all too soon the group are flopping back on board, to struggle out of their gear for lunch. The tuna is magnificent.

After lunch we move on to another dive site where the coral shelf is marked by a large fixed buoy. This is Turtle Bay. Throughout the trip the group has been warned not to touch or even brush against the coral. Here we find out why. The slightest touch can kill growing coral and diving has damaged some reefs, including this one, irreparably. The coral is dead, grey and lifeless, crumbling to nothing and supporting no life.

There are some compensations, however: dolphins are spotted and keep us company throughout the afternoon, circling the reef, and arcing through the water.

For the last dive together, the group drops down to the sea bed below to form a pyramid. This a dive game where the trick is to control your bouyancy and hang in the water - neither falling nor rising - using only your breathing. It’s a tricky manoeuvre and results in seething clouds of bubbles.

By the time the group surfaces, the weather has deteriorated. They change quickly under grey skies and a quickening breeze, as the boat sets course back to the relative comforts of Hurghada.

At the end of four days, all the pupils from Haydon passed PADI’s open water dive course. They are now able to dive - under supervision - anywhere in the world.

SAFETY FIRST: GOOD DIVING PRACTICE IN OPEN WATER

* Most adventure sports contain some element of risk but scuba diving is certainly one of those where the dangers are very real. Twenty-two divers died in UK waters alone last year, with 400 further incidents reported. It is a sport where the training needs to be thorough and where certain basic requirements need to be met.

* Diving is not a sport for young children. The mental and physical demands mean that The British Sub Aqua Club (BSAC) will not train anyone under the age of 14 while PADI only takes on those aged 12 and above.

* To dive you need to be physically fit. Anyone with an ear or chest complaint would automatically be excluded. Even those suffering from a cold could find that it is impossible to equalise the pressure in their ears on descent (as you would do when a plane lands, for example).

* The group from Haydon School learned to dive in the warm, clear waters of the Red Sea. Diving off the UK is a very different kettle of fish. The water is extremely cold, and visibility is usually limited. Both conditions can be potentially dangerous: cold divers use up their air supply more quickly and it can be easy to loose your diving buddy in murky water.

* PADI is a worldwide training organisation with a hierarchy of dive qualifications. The Haydon students took the four-day open water course.

BSAC also offers dive training which leads to recognised qualifications. Both organisations recognise each other’s qualifications.

PADI can be contacted via its website: www.padi.com BSAC, tel: 0151 350 6200 * Haydon School travelled with Scuba for Schools, tel: 0181 845 0945.

The group of 12, aged between 15 and 17 years old, paid pound;660 each for the all-inclusive trip.

Scuba for Schools also organises dive trips to the Mediterranean and in the UK.