In open waters off Australia's Great Barrier Reef, British diver Richard Neely and girlfriend Allyson Dalton tied themselves together as they drifted, trying desperately to be seen by spotter planes and searching ships. Barbara McMahon in Sydney reports on their dramatic rescue

A British holidaymaker and his American girlfriend who survived for 19 hours in shark-infested waters off the Great Barrier Reef, have told how a rescue helicopter failed to spot them waving frantically for help.

Richard Neely, 38, and partner Alison Dalton, 40, were last night recovering in hospital after drifting for nearly a day after their diving trip went horrifically wrong. The couple were part of a group of tourists on the 65ft catamaran Pacific Star and together with four other divers began exploring coral reefs around the Whitsunday Islands on Friday.

The two divers originally surfaced 200 meters too far from their appointed dive site but although they could see their boat clearly, those on board could not see them over the waves or hear their cries for help - and nor could the helicopter that arrived on the scene shortly afterwards.

From their hospital beds, the couple yesterday told how they had tied themselves to each other for warmth but began to lose hope after they drifted for nine miles from their boat.

'I truly thought we were going to die. Sharks were on our mind the entire time - but neither of us mentioned the "S" word,' said Neely, from Norfolk. 'We just had to stay positive and calm to help each other through the ordeal and not think about being eaten alive.

'To start with, we were just 200m from the boat, which normally wouldn't be a problem. We would just swim back,' Neely added. 'But the wind and waves had got up and it just took us away from the reef. We were signalling. I had my surface marker buoy, a very long inflatable yellow sausage about two metres long, and I had a whistle.

'We were shouting and whistling but nobody saw us. We saw other divers climbing back on to the boat and lifting out their equipment. The boat stayed where it was, on a mooring, but we just kept drifting further away. There was nothing we could do. We were helpless.

'We tried to swim to a big buoy we could stand on, but we couldn't make it. The current was too strong and there was no point in using up all our energy.

'We were still hopeful they would come and look and see us, but the waves had picked up and the sun was behind us, so maybe they just couldn't see us,' he said.

Neely's fellow divers searched for three hours but as night fell and it became too dark to continue looking for the couple, their boat headed back to shore.

At this point, said Neely, he recalled the book Bravo Two Zero, by the former SAS soldier Andy McNab for inspiration to stay warm. He used a six-metre length of rope from his marker buoy to tie himself and Dalton together.

Every half an hour, they huddled together, pressing their stomachs together for warmth through their wetsuits, then they would flip their bodies over to swim in the direction of the dive boat, as calculated by Neely, a diving instructor who was monitoring their position by compass.

It was the first time they did this, at 9.30pm, that they saw the first rescue helicopter. 'I shouted, "Look, look, there's a helicopter. They're here. They're coming for us",' said Neely. 'But they didn't see us. It was devastating to see them go round in their search pattern and then fly off into the distance.

'But we assumed they were going to refuel. I kept reassuring Ali they would come back. Then we would have a cuddle and get more body heat and then fin for a while and cuddle again.

'Sure enough, they came back every 45 minutes, did the same kind of search pattern, but I think with the wind and the two-metre waves, we weren't getting any closer.

'They obviously hadn't realised we had drifted so far. When the choppers stopped flying around at about 2.30 to three o'clock in the morning - we had no choppers for about three hours because the weather was so bad - both of us lost it. We had a lot of silence. Both of us would catch each other with our eyes shut, about to give up.

'I was aware we had been in the water for 19 hours by the time we were finally rescued. From the start, I told Ali, "We are going to get through this." I told her we were going to get very, very, very cold and we just had to be super-strong and I convinced Ali we could survive.

'All through the night, we were sharing body warmth. If I could see Ali getting weak, or Ali could see me getting weak, one of us would shout "I love you" to get a response so we knew we were awake.

'I really didn't think I could make it through the three, four, five o'clock time. Nor did Ali. We were hallucinating, seeing everything from robots to reefs and colourful fish in the sky and speaking a bit of gibberish.

'At that stage we thought we might close our eyes and sleep forever. But I told Ali we have a young relationship and we have far too much more to do with our lives. She is the most amazing person I've ever met and we will go on and live our lives the way we are meant to.'

During the night, said Neely, he thought he was going to die. 'But once daylight was coming, along with warmth from the sun, we thought, "OK. We're going to get picked up." But then with all of the choppers going past us but not seeing us, our hopes faded.

'We thought, "Oh my God, please - how can they not see us?" and we thought over the next two hours maybe we were not going to be picked up that day. I wouldn't have been able to last into the next night. We had bad moments. In the morning the shark thought popped into my head again. But I thought, "Rich, don't even go there."

'I said to myself, "This is really, really bad. This is a major drama. We're going to be on television." That kind of thing. We had to actually admit to ourselves we could die here.'

Then, at 8.40am yesterday, suffering from hypothermia, they were finally spotted - just after a highly-venomous sea-snake reared up in Dalton's face, forcing the rescue helicopter to winch the rescuer back up and move away.

'It startled me as it put its head out of the water and its face was in my face,' said Dalton, who runs a British-style pub in Sacramento, California, and is a qualified dive master. 'They are one of the most deadly poisonous snakes in the world, so I quickly swam away from it,' she added.

On the helicopter, they were wrapped in blankets and foil covers to help combat hypothermia and given small sips of water by a medic to rehydrate them.

After medical checks on nearby Hamilton Island, the exhausted couple were flown to a hospital in Townsville, Queensland, but released after several hours' rest and recuperation.

Dalton, who has been dating Neely for just nine months, said the experience had shown her what an amazing man he was. 'I think we saved each other's lives. Richard is an amazing man. I would not be here without him,' said Dalton. 'This terrible experience has definitely brought us closer together. We had an amazing relationship before, but to survive something like this together is bound to tie us as one forever.'

Darren Bobbin, a crew member on a rescue helicopter, said his team had searched for six and a half hours during the night using night-vision equipment. 'Things were not looking good. We went back to Hamilton Island to refuel and then we went back out again. All of us had a search grid to cover and we were going back and forth and then we heard one of the other crew say, "We've got a visual of two survivors".'

Bobbin and his crew then helped with the rescue. 'The woman was even able to joke,' he added. 'We asked them for a photograph and she said something about her hair not looking right because she'd spent so much time in the water.'

Last night, Neely's father Stuart said his son had called to say that he and Alison had been rescued from the sea in Australia. 'Then when I switched on the television I saw footage of him inside the helicopter. If he hadn't warned me I think I would have fainted on the spot. He told me they had been in the water for 18 hours - and there were a lot of sharks around.

'He and Alison are both being treated for hypothermia - it is a long time to be in the water, even in a wetsuit. I am just so relieved that they are both safe.'

Adventurers who cheated death

· A retired surgeon survived a fall of 200 ft earlier this year after an avalanche hit him in Scotland. Bill Church, 61, had been climbing the Black Spout Gully in Lochnagar and was 30ft from the top when a cornice broke above him and the resulting torrent of snow swept him away.

It took four hours for him to crawl across the snow to a first-aid hut. A mountain rescue team found him wrapped in a sleeping bag in sub-zero temperatures the next day. He miraculously escaped with just a broken left ankle.

· Adventurer Steve Fossett - who was declared dead after going missing in the Nevada desert last year - made a disastrous fourth round-the-world balloon attempt in 1998.

At the 15,000-mile mark, his balloon caught fire during a violent thunderstorm at an altitude of five miles high. He was plunged into waters near the Solomon Islands and spent the next 20 hours under the twin threats of shark and crocodile attacks.

· A swimmer survived an attack from great white shark by poking it in the eye as it dragged him through the water. Jason Cull, 37, was swimming off Albany in Western Australia two weeks ago when the 12ft shark tore two chunks from his left leg. He told the Australian newspaper: 'I found its eye and stuck my finger in. That's when it let go.' He was rescued by a lifeguard.

· A rock climber in Utah had to cut off his own arm to free himself after he became trapped under a fallen boulder. In May 2003, Aron Ralston spent five days pinned down in a canyon in the west of the state before he decided that he would have to amputate his own arm below the elbow using a pocket knife. The 27-year-old then escaped to the bottom of the canyon and walked for five miles before finding help.