It’s 11am on Monday at the Angel branch of Virgin Active in north London. I’m blinking the sweat out of my eyes at the water cooler, looking around at the packed cross-trainers, when it hits me: “Where did all these men come from? Don’t they have jobs to go to?”

Well, no, actually. Three months ago, the daytime vibe here was decidedly yummy mummy. Or studenty. Or gay. But in the past few weeks, the place has been besieged by thirty- and fortysomething straight men who have lost their jobs. Estate agents, recruitment consultants, chefs — it’s easy to spot them in their threadbare trackies and old T-shirts, complexion transforming from grey to peachy while their self-esteem hits rock bottom.

It was bound to happen. Since the scythe of recession got swinging, newly jobless men have been shuffling around Britain’s town centres on weekday mornings like prematurely retired racing dogs. You can spot them nervously sipping cappuccinos or hanging in morose little groups outside the local hardware shop. Watching them on the treadmills — literally going nowhere — is depressing. They have gone from power lunches to power shakes, from Bloomberg monitors to MTV, from having a ball to being in danger of losing theirs. And that’s only for an hour or two each day at the gym — what are they doing with the rest of their time?

“It’s like he has a secret life,” panics Catherine, a 37-year-old corporate lawyer. Catherine isn’t her actual name — she asked me to change it as her husband (I’ll call him Ben) hasn’t got around to telling his parents that he was sacked from his job at an investment bank in January. “It was a huge shock for him. He must have worked 80 hours a week for more than 15 years. The day they let him go, he said to me, ‘The hardest part is, I don’t actually know what to do with myself tomorrow.’ ”

So, what did you do, I ask Ben. “I slept,” he says, “then I went to the cinema, read the papers, called a mate who was given the chop before Christmas and we went for a drink. There were four of us at the pub, all ex-City guys. They said, ‘Don’t worry, mate. You’re about to have a lot of fun.’ ”

Fun? “You bet,” Ben says. Apparently, the three former bankers had already dubbed themselves the Musketeers and have spent the first few weeks of 2009 on a rollercoaster ride of lunchtime martinis and paintballing. Charles — who was laid off in December — has two kids and thought he would get rid of the nanny after the first flush of freedom, but three months later she’s still clocking on. “I found there was just too much to do,” he laughs.

Of course, the Musketeers are the lucky ones. Their bank balances are buoyant from years of lucrative toil, to say nothing of decent pay-offs or a spouse still slogging away. I go to meet them on a Tuesday afternoon at a gastro-pub in Primrose Hill, where they are finishing up a long, boozy meal. “We’re the ladies who lunch,” cries Matthew, 41. “We do a different restaurant every week — all the places we used to read about in Style, but never had the time to try out.”

Larks aside, there’s an air of enforced jollity. Jokes are laughed at for a fraction too long and there is a distinct aimlessness about proceedings. How are your egos, I ask? Isn’t hitting the gym just predictable, alpha-male displacement activity? “Yeah, maybe,” says Charles, patting his newly toned tummy. “The ego thing is tough. I’ve probably started hanging out less with people I used to work with, or not going to anything social where might ask me what I do for a living. It’s easier to spend time with guys who are in the same boat as you, or doing your own thing.” Because you’re embarrassed to say you’re unemployed? “Well, um, yes,” he says. “It makes you feel like less of a man, doesn’t it?”

They have a rule that they turn off their mobiles when they meet up. “That way, nobody can nag us,” Matthew says. “We’re hiding.” It’s no surprise their wives and girlfriends aren’t wild about this. After some badgering, Charles gives me the number for his wife, Miranda. “I was hoping you could tell me what he’s doing all day,” she whispers from her desk at an architect’s firm when I call, “because I honestly haven’t a clue. I leave him watching telly at breakfast and come home 10 hours later and he hasn’t moved. He doesn’t clean the house and he only has the children for a couple of hours a day. I literally have no idea — and the Google searches on our computer are always deleted by the time I get home.”

So, internet porn figures heavily then, boys? “No comment,” replies Ben, while the others snigger. The place has cleared out, but they’re showing no signs of heading home. “I’m meant to e-mail somebody about a job this afternoon,” says Ben, “but it’s all so depressing. Maybe I’ll do it tomorrow.”

For a lot of men, and certainly for those with less money than this lot, the depression can run deeper — and the secret daytime behaviour takes on a darker hue. This can range from the obvious — sinking a few tinnies while watching Loose Women — to more serious crimes. A schoolfriend who was let go by a large internet company rinsed through his final pay cheque in a week of binge drinking. And with all that time on their hands, affairs are on the rise.

Craigslist, the internet site where you can advertise anything from a room to rent to music lessons, has seen a boom in its “casual encounters” listings. My personal favourite was posted by a recently sacked young man offering the ladies of London a “credit munch” to cheer himself up. But it isn’t only the web’s more outré nooks and crannies that you have to watch out for. Facebook is a demon.

“I found myself getting addicted to the old FB,” says Jamie, 29, who has been kicking around his flat in Manchester for four weeks, since he lost his office job at a leading supermarket. “I was catching up with all these old friends from school, and some old girlfriends, too. I have to confess, I went to meet one for a drink yesterday afternoon. As a friend, though.” And? “We ended up kissing,” he says. “It was just an innocent thing.” Tell that to your girlfriend. “Well, maybe I’ll keep that one to myself. This is going to make me sound like such a knob, but it was an ego boost. If I’m honest, I’ve been feeling pretty low, so just forgetting your life for a bit is a big temptation.”

One man’s girlfriend learnt that lesson the hard way. The 34-year-old analyst from London had been worrying about her fiancé’s state of mind ever since he lost his job as an accountant last November. On his third week of solitude, after noticing he was letting himself go, she came home early to surprise him with shopping bags full of ingredients for his favourite meal. “Well,” she scoffs, “I came into the sitting room and he was looking really shifty, tidying up the coffee table. He’d been sitting there doing coke on his own all afternoon.”

Not that she doesn’t sympathise — up to a point. “The trouble is, a lot of these men who have worked hard for years need to blow off some steam. But I want him to get a job now — and not only for the money, though that would be nice,” she sighs. “Part of it is low self-esteem, but I think he’s having too nice a time on his own. Why can’t he just get a job?”

Are any of you planning on going back to work soon, I gingerly ask the chaps back at the pub. “Definitely,” says Charles. “Just as soon as the money runs out, or the wife decides to give up work.” They roar with laughter while I wonder who will be the first to have an affair with his kids’ nanny. With this lot, it’s really only a matter of time.