Jeff Flint sat with his wife and two infant daughters in the lounge of the Pride of Kent as the ferry left Dover for Calais. The builder from nearby Faversham no longer had enough work to fill his time so was giving his family a day out.

He had paid a mere £10 to put his car below deck - about the same as it cost to park it in Dover all day. He planned to visit the on-board shop to buy some heavily discounted cigarettes and perfume for his wife, which the staff would deliver to his vehicle. The fare did not allow the Flints to disembark in France so they would simply turn around and come straight back, but no matter. They would have had a meal, enjoyed a change of scenery and some sea air, and saved enough on tobacco to pay for the trip. “It's a very good deal,” he said.

Mr Flint, 42, is a phenomenon known in the ferry business as a “car park shopper”. While this may not be everyone's idea of a great day out, it appears — at least in this corner of Kent - to be an increasingly popular pastime as Britain tightens its belt.

Dover has been Britain's gateway for centuries, the town whose white cliffs provided the name Albion and the port through which have swept armies of invaders, migrants and soldiers. In the past decade or two, as Britain's pumped-up economy generated jobs galore and sterling was king, it was the entry point for Eastern Europeans seeking better lives and a point of departure for hordes of Britons seemingly intent on snapping up every last chalet, gîte and villa in continental Europe.

It acts, in short, as a sort of social and economic barometer, and as such it seemed as good a place as any to start a journey through Britain to explore the consequences of these islands' financial collapse.

In the town of Dover, now a mere adjunct to the huge ferry terminal, the main thoroughfare is already blighted by a dozen empty shopfronts. The town was once awash with migrant workers but not so long ago the Dover Express reported that three illegal immigrants had been caught trying to smuggle themselves back to France on a Polish lorry.

It would be easy to assume that Europe's largest roll-on, roll-off ferry port would be equally depressed. After all, imports and exports are plummeting. With thousands of jobs disappearing daily, and the euro vying for parity with the pound, not many Britons would be heading for the Continent, surely. At most, a few disconsolate Czechs and Poles might perhaps be heading home having found that our streets are paved with dull, grey, litter-strewn concrete.

At least one of those predictions was quickly confirmed. “Freight definitely has suffered,” Mike Krayenbrink, director of port development, acknowledged. The number of lorries passing through Dover last year fell by 2 per cent to 2.3 million, and would have fallen a lot more steeply had a fire in the Channel Tunnel last September not halved its capacity for five months. The volume of cargo fell by 19 per cent, reflecting the slump in international trade. Imports of sand, gravel and other aggregates used in the construction industry fell by a whopping 24 per cent.

The surprise is the figures for passengers, cars and coaches. In January, 735,330 passengers passed through Dover, 14 per cent more than during the same month last year. The number of cars rose by 21 per cent, and coaches 20 per cent. The corresponding figures for December had likewise risen by 11, 13 and 9 per cent, while 480,000 passengers — many of them skiers lured by record Alpine snowfalls — used the port during last month's half-term fortnight, 15 per cent more than in 2008. The ferry companies offer several reasons why. Britons are taking cheaper holidays, closer to home, they say. Low-cost airlines are no longer so low cost. Many more French and Belgians are visiting Britain, attracted by the weakness of the pound. “I could talk the hind legs off a donkey explaining why it makes sense to take a ferry,” said Brian Rees, spokesman for P&O Ferries, and proceeded to do so as he extolled the savings to be made by four skiers packing themselves and their gear into a car instead of flying and renting a vehicle.

The queue for the 11.10am weekday sailing to Calais included a respectable 66 lorries (half of them Eastern European), 6 coaches and 60 cars. As the ferry set sail a cacophony of burglar alarms erupted from the more expensive of those cars.

My 557 fellow passengers included a party of pigeon-racers heading to Belgium, a group of A-level students bound for the First World War battlefields and a stag party from Swansea determined to paint Paris as red as it could given the dreadful exchange rate (its 15 members had brought £200 worth of alcohol with them). I found only one pair of skiers — retirees with time to kill — and not a single migrant heading home. Later, in a Polish food shop in Dover, I was told that the exodus had all but ceased because Eastern Europe's economies were even more desperate than our own.

The most interesting discovery, however, was that almost every other passenger seemed to have paid a fare so negligible you wondered why P&O Ferries charged at all. Many had paid £19 for a day return that included six free bottles of wine and a meal. Others were car park shoppers like Mr Flint.

They were a typically British lot — resolutely cheerful in the face of adversity and determined to have a good time. Sean Temlett, 42, a printer from Plymouth, expected to lose his job next week but was looking forward to a few hours in Calais with his girlfriend first. “You can just slump back and think that's it, or soldier on and enjoy yourself while you can,” he said.

In the ship's bar a middle-aged couple from Bristol were buying their first lagers of the day before stocking up on wine and tobacco. Both worked for an engineering company that had put them on two-day weeks. “We have lots of time but no money. We're just making the most of what we have left,” the wife said.

“Live for the day!” proclaimed Sarah Buck, 27, a cheery Debenhams supervisor, who had just taken out a £60,000 mortgage on a house, booked a holiday in Las Vegas and driven down from Ipswich with four friends for a day trip to Calais.

There is method in P&O's madness. The giveaway fares “are designed to get volume on to the ship and then get as much money out of the passengers as we can”, Deane Robinson, the Pride of Kent's retail manager, acknowledged with refreshing candour. The on-board shop offers highly competitive prices because it buys in bulk and charges French duties on alcohol and tobacco. A packet of cigarettes, for example, costs about £1.40 less than in Britain. The average passenger spends £11 a crossing in the vessel's shop, bars and restaurants, and in a single year the Pride of Kent earns about £19 million from those enterprises.

Car park shopping is an idea that seems custom-made for recession-hit Brits, and it is not hard to see it taking off. For the millions who became addicted to retail therapy, foreign holidays and abundant alcohol during the good times, a quick, cheap trip across the Channel with cut-price fags and booze and no exchange-rate worries may soon be all that they can afford.

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