You know the routine. You log on, sign up and then scroll though the ads, scanning the descriptions and judging the photos. Should you go for the “gorgeous European” or the “generously proportioned American”? Or perhaps you are the “London beauty” who has just found her “Paris match”. All the time, you are looking for the one you really fancy, the one that might just turn out to be The One.

These are not websites for lonely hearts, they’re for people in search of holiday homes. And free holiday homes at that. That’s right, free. A villa in Valencia? Yours for nothing. A palace in Pacific Palisades? To you, zilch. An apartment overlooking Sydney harbour? Have the soft-top in the garage, too.

The catch? Well, there is one little thing. While you’re indulging in your new pad, quietly congratulating yourself on having blagged an entire holiday for the price of the flights, back home your own place is under siege. Someone else’s son is running riot through your kitchen, his elder sister has pawned your television and the scoundrels’ parents are taking crowbars to your cat, having already written off your car.

At least, if you’re the anxious type, that’s what could be going through your head: a house exchange isn’t for everyone.

“Some people find it difficult to get their head around having someone else in their home,” says Lois Sealey of Home Base, one of the main house-swap agencies in the UK. “You’ve got to be the sort of person who is relatively relaxed — the sort who believes in trust.”

Put simply, house-swapping works on the principle that if you are on holiday, your own home is empty. While it is, someone else may as well use it. And that someone might as well be from a place that you want to go — whose own house will be empty for you to use.

The most obvious advantage of this kind of holiday is financial, and the savings can be vast. For example, a family of five seeking a fortnight in a Tuscan villa in July 2005 could opt to pay £1,260 for the three- bedroom Podere Il Cocco, outside Siena (www.rare-tuscany.co.uk), excluding flights. Alternatively, they could bag a four-bedroom villa with pool in the same region for nothing by house-swapping through Home Base Holidays (ref: HE15506). The family’s only outlay would be the £29 agency fee. Swap cars, too, as many home- exchangers do, and a holiday can cost less than a quarter of the price of the same trip with a rented property and vehicle. Renting a Renault Mégane in Tuscany with Holiday Autos would set you back £456 for two weeks.

“Quite simply, house swapping means that we can afford to take more holidays”, explains Rod Hirst, a retired teacher who, with his wife Mary, has done 26 swaps in all. “And when we are on holiday, we can afford to do more things. We’ve taken a helicopter ride over the Grand Canyon and an island-hopping trip around the Whitsundays — both using money saved by having free accommodation”.

For others, it’s about more than simply saving money. Jon and Ann Rebak from London did their first swap this summer, exchanging their north London house for a place in northern California. “It went extremely well,” says Jon. “We used their home only for a few days at the beginning and the end of what was mainly a touring trip, but the time in the house was definitely the most relaxing. It can get exhausting staying in small motel rooms with a family. In the house, we weren’t tripping over each other in the same way. We could relax.”

John and Marie Hennessey from Ballinglanna, near Cork, go further still: “When you swap houses, you are parachuted straight into a community. Neighbours and friends of the family you’ve swapped with show you around. You can avoid the tourist traps, cut to the chase and have a much more fulfilling holiday than if you are staying in anonymous hotels.”

Increasingly, too, people are being more adventurous about the kind of swaps they set up. For their four-month trip to Australia, Margaret and Ron Fox from Ashford, Kent, arranged three consecutive house exchanges: in Adelaide, Perth and Mooloolaba, in Queensland. “A relative sorted out the handovers this end,” says Margaret, “while we had a three-base holiday in Oz.”

So, what holds most people back? The “what ifs”, of course. What if your swapees burn your house down? What if they steal your car? What if they smash your favourite sculpture? What if they simply pull out at the last minute?

These are justifiable concerns, admits Caroline Connolly of HomeLink, another of the house-swap agencies, “but they are all much, much rarer than people imagine”. “What you have to remember is that while they are in your home, you are in theirs. People do as they would be done by.” Although the home-exchange agencies don’t vet potential swappers, they do operate a monitoring system. “It doesn’t happen often, but if we get more than one bad report about someone, or a single serious complaint, we’ll strike them off the list. We don’t wait for people to burn a house down before taking action.”