It is a nippy but bright December morning and a low sun is spilling gold on the comparatively calm surface of the English Channel. The thermometer in the doorway of the changing room is registering just over 44F or 8C.
John Ottaway, the chairman of Brighton Swimming Club, is not going to let "a bit of a cough" put him off his daily dip. He is one of the "hardcore" half a dozen or so members who turn up at 11.30 every morning, whatever the season. Most are either retired or able to work flexible hours. Every year they are joined by another 25 or so for whom Christmas just wouldn't be Christmas without a bracing plunge into the icy waves. "During the rest of the year we're rather confined to weekends because of work commitments," says the club secretary, Avon Spry.
She's one of eight women members who swim in the sea all the year round. There are no women this morning.
The men strip off and by the time they have emerged from the bunker and picked their way across the stones, Mr Sawyer's pink swimming cap is just about visible in the middle-distance. His friend, Henry Law, is bringing up the rear. Mr Law and Mr Sawyers share the same age, 59, and both suffer from debilitating back pain.
Mr Sawyers's eagerness to be first in the water is a reflection of the relief he finds in an environment that would be purgatory to most of us. "Swimming in the sea is the only circumstance left to me where the pain is not intrusive," he told me before taking the plunge. "I'm keeping my mind so occupied with the strength of the current and the height of the waves that I have no room to acknowledge that I'm in pain. Like every regular sea-swimmer, I have an awareness of being caught up in the natural rhythms of the world."
A cultural historian, Mr Sawyers has traced the origins of the swimming club back to 1858. His own great-great-grandfather was among a small body of traders from North Street who took lessons from a one-legged merchant seaman called Captain Camp. But sea-bathing in Brighton goes back to the previous century when it was pioneered as a "cure" by one Dr Richard Russell. Writers and philosophers of the day thought the benefits could be more than simply physical.
More than 200 years on and the writer Brian Behan, brother of Brendan, has offered a rather less elevated explanation for his habit of swimming in the nude all the year round at the age of 73. "It's good for the gonads," he has been said to relate. He was recently startled that the sight of his naked body had caused a passer-by, suspecting suicide, to dial 999 and set off a full rescue attempt.
Behan swims a little further up the coast from the Brighton Swimming Club, whose members are decently, if scantily, clad on this sharp winter morning. First to re-emerge from the waves is Norman Saddleworth, 81, a former official receiver in the High Court. "My heart's feeling a bit tight," he says, "and the doctor's told me not to stay in too long." Mr Saddleworth celebrated his 80th birthday by swimming round the pier, a distance of three-quarters of a mile. "Luckily, it was in July," he concedes.
It was around that time of year that Tony Brannick, 62, a school caretaker, joined the club. "When I found out they did this all the year round, I thought they must be mad," he says. "But I kept going though the autumn and acclimatised myself. You have to build up to it or the cold would be too much of a shock to the system. Well, soon Christmas was on the horizon and I thought I might as well carry on."
So is it addictive? "I think it might be. I sometimes come down here feeling depressed and looking for excuses not to do it. But I know I'm going to feel good afterwards. It's like a mental glow," he adds, gingerly picking his way back across the stones in bare feet.
Everybody agrees that the walk back from the sea is the worst part. Angus Kennedy, who works shifts at Gatwick, remarks through chattering teeth that "it's like stepping on red-hot pokers. When your feet are so cold, that's what it feels like," says Mr Kennedy, who knows he's going to feel the better for it any time now.
"It does promote a feeling of well-being. I don't enjoy swimming baths. This is much more challenging and you can swim without interruption."
At 36, Mr Kennedy is very much the spring chicken. The average age of the year-round sea swimmers is 55. Yet there has been only one fatality in recent times. "An old boy had a stroke while he was drying himself off and expired in my arms with a giggle," Mr Sawyers recalls. "There was something he found enormously funny. I think he was determined that this was the way he wanted to go."
Attracting new blood has proved problematical. "Youngsters are a bit soft. They're used to heated swimming pools and continental holidays," mutters Mr Law. Although almost fully dressed, he is still shivering violently. These people are not just stoical but heroic in the way that they daily pit themselves against the elements.
Outside the bunker, a middle-aged Australian has been watching proceedings with bemusement bordering on astonishment. "How can they do that?" he asks. "When I went in the sea off Melbourne a few weeks ago, it was cold enough. It's summer at home, but I had to wear a wetsuit."
Well, it's good to know that there's at least one outdoor activity where we can show the Aussies a thing or two.