FOUR years ago, my husband decided that our X-reg Ford Escort looked too disreputable even for him, and we bought a new car. What to do with the old one? It was sound in wind and limb, but so battered that its value was negligible.

The answer proved to be to share it. We did this first with a friend who lives three streets away, then with our immediate neighbours. Four years ago the car was silver. Now it has two red doors and one white, and the bumpers are held on, very effectively, with parcel tape. But it goes a treat.

Car sharing flies in the face of the trend. In the past 20 years, multi-car homes have been the biggest growth area for car ownership, with about 4 million extra cars. By 1990, nearly one in four households had two or more cars - up from just 7 per cent in 1970.

If the recession hasn't reversed the trend, Norman Lamont's tax timebombs may do so in April, when most two-car homes must find pounds 500 a year or more to cover delayed tax and National Insurance increases. So cutting down from four to three cars between two homes offers big savings at an opportune moment for the relatively rich; and for the less well-off, sharing one car offers at least partial access to independent transport.

Sharing isn't easy with a new car that is your pride and joy. But sharing a two- or three-year-old vehicle would save pounds 500- pounds l,000 per household per year out of after-tax income - nearly half the running costs shown below (although depreciation and service costs are bound to be higher). But before rushing round to the neighbours, answer honestly five questions:

1. Would you mind terribly if your neighbour smashed up the car and destroyed the no-claim discount? (I came back from holiday once to find the car doors damaged beyond repair, my co-sharer recovering from concussion, and the perpetrator vanished. Driving for a month with two doors jammed shut and thereafter with doors of different colours had a certain disreputable chic, while climbing over the passenger seat for three or four weeks saved a fortune in aerobics classes. My co-sharer had the guilt and the trouble of replacing the doors.

2. Do you like everything in your car to be kept just-so?

3. Can you be punctual?

4. Will relations with your neighbour survive niggling annoyances?

5. Can you ignore local gossip?

If the answer to Questions 1 and 2 is 'No', and the answer to Questions 3, 4 and 5 is 'Yes', and if the same goes for your proposed co-sharer, read on.

I did not find the legalities of car-sharing complicated, despite experiences with the police arising from the Escort's bashed-up appearance. My husband is the owner of the car I share, and the insurance was in his name. The policy allows other people to drive it with his permission. This arrangement, where one sharer owns the car and the other contributes to costs, is probably simplest, especially where the car is old.

Another option is joint ownership. This has the advantage of automatically splitting depreciation, and sharing legal responsibility for the car being roadworthy. But this could be a lawyers' paradise. It seems that 'keepership', not ownership, is what matters for many purposes. To give you a flavour, here is a telephone conversation I had with a helpful expert.

Expert: Perhaps I can read you some extracts from Wilkinson's Road Traffic Offences, 12th Edition. This states that 'owner' is not defined in the Vehicles Excise Act 1971: the person required to be registered as the owner is the person by whom the vehicle is kept.

Me: In other words, if the owner is not the keeper then the keeper is the owner and the owner isn't?

Expert: That's right.

Theoretically, one must inform the Secretary of State for Transport every time the keeper of a car changes. If I ever bought a car specifically to share, I should put names and addresses of both sharers on the vehicle registration document and defy the bureaucrats to reduce them to one.

I suspect that what they and the police want is one person at one address to be held responsible for anything the car does. But since they already accept husbands and wives - and, presumably, partners living at a single address - as joint keepers, they may have no legal reason for banning two names at different addresses. One could threaten them with action in the European Court of Human Rights.

There is a serious point about all this. Some weeks after our car doors were smashed, and the police were still seeking the hit-and-run driver responsible so that we could charge him for the repair, a couple of local bobbies in a crime-ridden part of central London had nothing better to do at 1am one night than to stop my co-sharer and to propose legal action against him because the damaged doors were sharp (they weren't very).

Prosecution was finally stopped after a visit to me by a sheepish policeman long after the doors had been replaced. He said that if it did go to court, my husband as owner/keeper could be liable for a three-point endorsement on his driving licence for keeping a car on the road when it was not in a roadworthy condition. This was a car for which he had no practical responsibility since I shared it with a neighbour while he drove our new car; and it was the neighbour who had been driving both on the occasion of the accident and when stopped by the police.

Despite this, as I said, I did not find the legalities of sharing complicated in practice. Other tips: I gave my sharers a photocopy of all legal documents (the moral responsibility for keeping the MOT/insurance up to date is then joint). The person whose name is on the insurance should give permission in writing to the other driver(s). In a newer car than ours, small knocks should be mended by the person in charge at the time. If one sharer loses a no-claims discount through another sharer's fault, compensation is needed: agree that in advance, too. Access to the original MOT, insurance, etc, must always be available to both sharers in case these are needed for presentation at a police station.

We found the best way of sharing was to agree the times in each week when the car would be deemed to belong to each sharer. When it was not 'my time', and I wanted it, I telephoned to see if it was in use, and vice-versa.

Would I do it again? With the right person, yes.

Cost of running a car per year

Total cost: Tax pounds 125; Insurance pounds 500; Servicing/repairs pounds 300; Depreciation pounds 800; Interest lost pounds 250; TOTAL: pounds 1,975.

(Guesstimate for a two- or three- year-old Ford Escort.)

Insurance is comprehensive. Interest is 5 per cent on pounds 5,000 and assumes a cash purchase. To calculate figures for your own circumstances, see 'Car Running Costs', Which? February 1992.

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