There is something about a used car that is intrinsically more interesting than a new one. That patina of age, the mystery of its history. Each used car is unique whereas a new car is simply the product of a giant sausage machine.

The other day a photographer friend gave me a lift in a marvellous old car: a Y-reg Citroen CX. It cost him pounds 700 and was in good condition, having been garaged all its life. As with all CXs, it rode with an insouciant gracefulness and suppleness, moving with the charm of a grand old dame rather than the inelegant loiter of a Doc Martens-shod teenager. (Too many modern cars have kick-your-butt suspensions, the upshot of tyres that are too big, to make the car look aggressive.)

After the experience in my friend's CX, I decided to play DAT (Dreaming with Auto Trader), one of the car enthusiast's favourite games. It requires merely a sense of imagination, a copy of a buyer's guide and a wet weekend when contestants have maximum spare time. Like most DAT contestants, I concentrated on what the trade likes to call "prestige marques". Also the bigger the better, because bigger cars tend to give better service in their dotage. Besides, big cars depreciate faster, so represent better used value.

Old Mercs and Volvos last better than any other big prestige cars but unfortunately everybody else knows this, so their used prices are higher. Mind you, there were some bargains about in last week's game. How about a 1983 Mercedes 380SE for pounds 2,950? (The last S-class was quite the loveliest Mercedes post-war saloon and probably the best made.) There were loads of good big Volvos for pounds 2,500 to pounds 3,000 but, deep down, I know I'd rather have a Merc.

Or a Jag. Jags have lousy residual values because they have lousy reputations for reliability. Last week's Auto Trader listed many of the last generation XJ40 series, one of the least reliable and thus fastest-depreciating of all Jaguar saloons, for less than pounds 4,000. There was an 1988 Sovereign for pounds 3,995, another E-reg Sovereign for only pounds 34,95 (OK it had only the anaemic 2.9 engine, but for this sort of money who cares if it is outdragged by mopeds from the lights?) and a 1987 2.9 XJ6 for only pounds 2,995.

Rolls-Royces also drop in value as fast as pebbles in a stream, and the old Silver Shadow is far more elegant than the latest boxy Silver Dawn. A 1978 Shadow II for pounds 6,950 seemed the pick of the bunch but there were many other Shadows for under pounds 10,000. That's less than 10 per cent of what you'd pay for a new Roller and with all the essential charms of Rolls- Royce motoring intact.

There weren't so many CXs last week but there were loads of big cheap Renaults, BMWs and Alfas. I love old Alfas because they look so great and they're fun to drive but I'd never buy one as main transport.Old Alfas are quite the worst made west European cars of all. Sometimes, even when playing the DAT game, common sense has to make a stand.

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