In his high-octane career as a business journalist Ed Mitchell interviewed five chancellors, six presidents and three prime ministers, including Tony Blair. At his peak he earned £100,000 a year, lived in a £500,000 house by the seafront in Hove, and took his family on lavish holidays to Cape Cod and North Africa.

But - incredibly - his 33-year career as a finance reporter at ITN, BBC and Sky, and his middle-class background, failed to prevent him from ending up sleeping on a park bench.

The irony is not lost on Mitchell. He admits it was “daft” as a business journalist to rely on the never-never. As we walk around the back of a nightclub called Babylon Lounge to the bench he now calls home, he still can’t believe it has come to this. “I had a false sense of security, that it couldn’t happen to me. I was naively optimistic and thought that something would turn up. And it didn’t.”

It’s a cautionary tale for any of us who think nothing of putting those Christmas presents on the credit card.

Sheets of cardboard are neatly wedged inside what looks like an oversized bus shelter. A stone’s throw from the club is the bleak grey shingle of Brighton and Hove beach. It is bitterly cold; after 10 minutes I am shivering uncontrollably.

Mitchell’s pillow is his rucksack in which he carries photographs, a Swiss army knife, a tin opener, enough clothes for five days and, ironically, credit cards - “for ID purposes. Someone stole my passport”.

His old three-bedroom, bow-fronted semi is no more than 800 yards away, where Mercedes and BMWs line the street. “When I first slept rough in March I was nervous: I’m not a professional rough sleeper and it was a very stiff learning curve. The first place I slept was in a walled garden. I thought it would be safe and that nobody would come along and beat up a tramp.”

Mitchell is so well presented in a brown leather jacket, white polo neck and trendy brown shoes (“£12 from Asda”) that it’s hard to believe he really is what he calls a “dosser”.

And yet the story is frighteningly conceivable. When he was made redundant from the US network CNBC in 2000 he had unsecured debts of £50,000 through bank loans and credit cards.

The classic middle-class nightmare became a grim reality. “It’s the typical story. I had thought I was rich in the sense of bricks and mortar - I was in full employment and my mortgage repayments were £600 a month,” says Mitchell, now 54, “but when I was made redundant I couldn’t find another job. So every offer that came through the post for interest-free credit cards, I thought: I’ll have some of that.”

It was supposed to be a temporary measure. He had his wife Judy and two children - Alexandra, now 24, and Frederick, 22 - to support. He would use one card to pay off another, but had soon amassed 25 cards and the repayments spiralled out of control. He remortgaged the house three times and ran up debts totalling more than £250,000. His minimum monthly repayment on one card alone came to £1,000. For six years he kept up appearances, moving to a smaller house in nearby Portslade and taking the odd short contract: “But I realised it would have taken five lifetimes to pay off my ultimate debt.”

He was officially declared bankrupt on November 20 last month. After 25 years of marriage the financial pressures proved too much and his divorce was finalised this autumn. His house had been sold within two days. Judy took their son to live with relatives; Mitchell, not wishing to burden his daughter or 83-year-old mother, spent the odd night with friends, then turned to the streets.

He now survives on a £52-a-week jobseeker’s allowance, which he spends on his bus pass, crediting his mobile phone and buying food. He relies partly on handouts from Brighton-based charities such as the Off the Fence Trust, which hands out sandwiches, coffee and Mars bars to the homeless every evening.

But he refuses to be seen as a tramp: “The stereotypical tramp is unshaven with a grubby hood, shoe-laces undone, with a sleeping bag, aggressively begging. But there are plenty of well-spoken homeless who try and keep clean. If you don’t want to fall through the cracks, you need to shave, shower, not look like a dosser - otherwise you’re sunk.”

He admits, though, that he sleeps ‘ferally, with one eye open”. He goes to bed at 8pm now it’s winter, and gets to sleep by drinking cheap cider. He has about three hours’ sleep a night, “which is difficult in terms of getting a job even stacking shelves. You’re not at your best”.

Alcohol, he admits, has been a big factor in his fall from grace. His first job in journalism was at Reuters on Fleet Street where drinking, he says, was a crucial way to get the story. The Today presenter John Humphrys remembers him as an eager young reporter. “I told him not to go into TV journalism,” he recalls. Sound advice.

At his worst he was drinking five times the present recommended weekly limit of 21 units. One of his employers sent him to the Priory rehab clinic.

Christmas Day will be spent with the other homeless who congregate at “Hotel Babylon”, which will be hard, he says. “At Christmas you think of the warmth and comfort of the family home. You can’t do this for ever, the other dossers look so much older than their age.”

It’s hard to imagine this well-spoken Durham University graduate blending in with the local drunks, but he is fastidious about maintaining those middle-class standards.

Next to the nightclub is a public lavatory that, says Mitchell proudly, “has won best toilet in the southeast five years in a row. It has hot water, a mirror, well-cleaned lavatories”. He also saves for haircuts and goes to First Base, a housing trust that provides showers, hats and “fantastic porridge”. He uses its washing machines, and stores his sleeping bag in the outside cupboard of a local acquaintance so that he doesn’t drag it around.

He has the air of the schoolboy embarking on his gold Duke of Edinburgh challenge, but with the urbane charm of a professional broadcaster. His days are spent looking for work or in the library, where he reads the papers and is midway through an Ian Rankin novel. He does admit to feeling miserable sometimes though.

It took him a while to persuade the fellow homeless that he really was sleeping rough. “On the street it’s survival of the fittest. There is camaraderie, but if you lose touch with the pack, they’ll get you.”

His street buddy is a former millionaire turned alcoholic. Mitchell grandly predicts that the 21st century will see many more white-collar tramps. Ever the business journalist, he launches into an appraisal of the sub-prime market and fall in house prices. “A bad debt tsunami will hit this economy,” he warns.

“I haven’t thought about suicide, though I know other people in my situation have,” he says. “If life is a soap opera, I want to see the next episode.” With rumoured agents in the pipeline and a phone so red-hot “it’s been the only thing keeping me warm the past few days”, I suspect we’ll all be tuning in for the next instalment.

Times recommends

• Tewkesbury: when the memories flood back
• How I lost the gift of joy for a while
• The A-Z of winter style rules