Brighton mum Fiona Southwell is attempting to achieve a lifetime's ambition and break the world record by becoming, at 50, the oldest British woman to swim the English Channel. She talks to Ruth Addicott about her incredible training regime, the battles with jellyfish and how a Jaffa Cake could just see her through.

Swimming the English Channel isn't the most leisurely way to spend a 50th birthday, but for Brighton mum and former teacher Fiona Southwell, it is the chance to fulfil the ambition of a lifetime.

On July 14 , Fiona is hoping to break the world record by becoming the oldest British woman to swim the Channel. She has fought her way through ten-foot waves, clumps of jellyfish, even a foam mattress, and it's going to take more than a seagull perched on her head to stop her now.

The gruelling 20-hour trip is equivalent to running two marathons back to back in terms of endurance. It has taken four years of preparation, an intensive training regime and a change in diet which has seen her swap her slender female frame for muscles the size of Arnold Schwarzenegger's.

Not a lover of pasta, she has had to bulk up on carbs with a bowl of porridge at 5am and pasta every night at 9pm.

There have been tears, there have been tantrums - and plenty of muscles pulled in between, but she is putting all that behind her in order to reach France and raise money for an autism charity.

"I have always wanted to swim The Channel ever since I was a little girl," she says. "It's not just about physical ability but mental attitude and I feel now is the right time."

Swimming has been the focus of her life for as long as she can remember, whether it was winning her first race at the age of eight, swimming for the Brighton Shiverers club, for her county or at international level.

Fiona is also no stranger to the sea, being one of those dedicated sea swimmers who venture out every morning.

The training for her Channel attempt, however, is a lot more strenuous, having to build up sufficient stamina to be able to stay in the water for up to 20 hours. She has two professional trainers - former Channel swimmer Mark Shepherd and Freda Streeter, whose daughter Alison, MBE, swam the Channel 43 times.

Fiona does three power swims a week (two hours each) and three long-distance swims - one from Shoreham to the Palace Pier, Brighton, another from the marina to the West Pier and back, and another in Dover Harbour which can last anything up to eight hours.

"It's lovely to reach land," she says, already exhausted just from training.

"I feel like I'm permanently swaying."

Wearing nothing more than a bathing suit, hat, goggles and earplugs (rules state you cannot wear a wet suit), Fiona has also had to get used to all sorts of conditions, battling the waves in heavy fog, wind and rain. On one occasion, the temperature was four degrees and there was snow on the beach when she set off.

"That was quite a quick swim," she admits. "My toes, fingers and arms were frozen."

The 21-mile Channel trek will seem like bathwater by comparison, as she points out, and is unlikely to dip below 13 degrees.

Aside from swallowing copious amounts of sea water, Fiona has also become acquainted with "the claw", a term used to describe the condition when the hands and fingers get so cold they get stuck in a claw-like position.

"I got the claw most of the winter when I couldn't bend my hands when I got out," she says. "Like most female swimmers, I tend to suffer from a cold neck, hands and feet.

With the men it's their testicles. Some wear a couple of pairs of trunks, especially in winter."

Fiona has had plenty of highs and lows but her darkest hour so far was the six-hour qualifying swim in Gozo, Malta. She was the only woman taking part. There was a main support boat, two fast dinghies, three male swimmers in front and two others behind.

Despite the choppy waters and spotting a huge ray beneath her at the start, it wasn't until five hours into the swim things really began to get tough.

When one of the swimmers got into trouble and the support boat went to his rescue, suddenly she lost sight of everyone.

"The waves were so huge, all I could see was huge clumps of jellyfish in every direction," she says.

"Everywhere I swam to try and avoid them, they were there."

Although she has swum with (and been stung by) jellyfish in Dover, these were different.

"They were absolute bastards, really nasty," she says. "They were enormous, they had purple tentacles and just burnt you. I had a whole clump stuck to my face at one point, and the more I tried to beat them off the worse it got. I was stung on the face, neck, arms, legs - everywhere. It was horrendous.

"I was into my fifth hour, I hadn't seen a soul for over an hour and I'd been stung from head to toe. When you're alone in unfamiliar open sea like that, it's petrifying. You have got to just work on your mind. You can let it hurt or simply ignore it.

"The waves were so high I could hardly see in front of me, let alone to the island of Malta. It was miles away. All I could see was a dot in the distance. I knew I had to carry on, I just put my head down and did it.

It was the loneliest, scariest moment of my life."

So relieved it was over, when she reached the shore, she sprinted back to the boat, crying.

Fiona still bears scars from the stings today, although she didn't come off as badly as some of the other swimmers.

"One man had three great big trail marks across his chest which looked just like a woman's finger nails," she recalls.

Jellyfish aren't the only obstacles she has encountered on her training sessions. She has swum into everything from buckets, bottles and planks of wood to a huge foam mattress, which scared her half to death at the time, fearing it was some sort of sea creature. She has even had the occasional seagull land on her head.

During the Channel crossing itself, she will have to contend with everything from canoeists in Dover Harbour to oil tankers and passenger liners.

Even Mark Shepherd, her trainer, nearly collided with a Russian tanker in his attempt. "It's the busiest shipping channel in the world," she notes.

Swimming in the dark for five or six hours is one of the things Fiona is looking forward to least. Having to wait for the right tide, she is expecting to set off at 9pm.

"Everyone has said it's better to swim into daylight as it's really exhilarating and gives you an energy boost, but swimming in the dark is my main worry," she confesses.

With just two little lights strapped to her back, Fiona is hoping to complete the swim in 16 hours, but it could take anything up to 20. It will be down to the official to decide if she should stop - if she is incoherent or going into hypothermic shock.

Her trainer, Mark Shepherd, is only allowed to get in the water twice during the crossing, when he can swim alongside her for up to an hour to boost her morale and help her pick up speed. She'll also have a high-protein energy drink every half hour and occasional comfort foods, her favourites being a Turkish Delight or Cadbury's Swiss Roll.

"Your tongue gets so swollen, it's difficult to chew and you lose all sense of taste," she says. "A Jaffa Cake is good because the sponge soaks up the excess sea water."

Asked what she is looking forward to most, she says: "Standing on those rocks in France. I always enjoy the last hour. I have a huge adrenalin rush."

Fiona will be accompanied in the boat by her trainer Mark, her open water trainer Adrian Bates, a pilot and an official. Her husband Peter, daughters Bianca, 24, and Pippa, 22, and son Randle, 18, will also be on board cheering her on.

"They'll have to take sleeping bags, pillows and enough food to last them 20 hours," she muses.

Her own plan is to stay positive and take it one step at a time - focusing on her next Turkish Delight rather than France. Even music helps and she finds herself mentally playing out songs by Marvin Gaye and Julie Andrews to spur her on.

"I just shut down and go into a hypnotic dream," she says. "It won't be my will that stops me but the elements. Anyone who knows me knows I'm a hard woman. I've had the training, I have the wit, I have the dream. It is down to Poseidon."

When things get really tough, however, Fiona will be replaying the words of one of her closest friends and fellow sea swimmers.

"If I feel I can't go on, my friend always says to me, Fiona, it's only a swim. It's a bloody long swim, but it's only a swim'."

She pauses before adding: "My will won't let me down."