If you keep your eyes peeled while out and about in west London you might catch sight of a little silver 1.6 Ford Escort Ghia. The unassuming hatchback with 80,000 miles on the clock would typically be worth less than £200. Two years ago it was sold for an undisclosed figure closer to £50,000.

The car was Prince Charles’s engagement gift to Diana in 1981. And the astronomic surge in its value represents a phenomenon taking place across Britain, where celebrity connections have never been so highly valued. Discovering your car has a VIP past could land you a lot of money and, it seems, the more ghoulish the link the better.

The famous Ghia was bought two years ago by an anonymous buyer as a gift for his daughter to get about London. It was bought from Keith Lawson, a dealer in antique clocks from Norfolk, who had bought the car in 1995 as a present for his own daughter. It cost him £6,000, but after Diana’s death the value rocketed.

Tim Schofield, head of collectors’ and historical cars at Bonhams, says that an increasing number of bidders are in pursuit of far more than four doors and a steering wheel. “When people bid for celebrity-related cars, it’s a statement about themselves,” he says. “And the more emotional and macabre connotations a car has, like the death of a celebrity, the more desirable it can be.”

Underlining his point was the sale this month by Christie’s of the Austin Princess VA135 hearse used in Churchill’s state funeral. Its history meant the car sold for £5,875, around three times the value it would merit otherwise.

Last week Diana’s 1978 Range Rover was sold at an auction in Buxton, Derbyshire. The car, in which she had been regularly photographed, went for £2,600, which must be something of a bargain, even if it is 75% more than the ordinary value of such a car. But it is cast into the shade by another Diana-linked car, the Daimler that carried her body at her funeral, which was sold by Coys for £90,000 — £87,000 more than its market worth.

Chris Routledge, managing director of Coys, has no qualms about handling such a potentially emotive deal. “At the end of the day we are a commercial operation, so any grounds for a moral argument don’t really come into it,” he says. Routledge, however, declined to discuss details of the successful bidder because, not surprisingly, the new owner wants complete privacy.

Routledge has handled other celebrity car sales. “We recently sold Eric Morecambe’s 1974 Rolls-Royce Silver Shadow, which he bought from new. It’s a lot more valuable if you can buy direct from the family, as it has more kudos. If a car has had 20 owners it tends to dilute the value significantly. The Rolls was worth £5,000 but we sold if for £36,650 to an enthusiast over the phone.”

In fact the “collectables” arm of every auction house in Britain is doing feverish business, with many believing it’s only a matter of time before an auctioneer begins specialising only in celebrity connections, as happens in America.

“I call it the Diana effect,” says Routledge. “When she died there was a surge of people buying things for the nostalgia factor, and it’s certainly spread. People have latched onto the fact that they can sell anything with a famous connection.”

It seems the bigger the cult status the bigger the cheque. But buyers must be shrewd. “The rise in interest has also meant some people trying to pass off unlikely machines as celebrity cars,” says Schofield of Bonhams. “Sometimes all they have is a photograph of a star taken next to a car at a golf tournament, so you have to be careful.”

Interestingly, experts advise potential speculators to avoid sports celebrities’ cars, which for some reason are not deemed particularly desirable. Also sold last week by H&H Classic Auctions in Buxton was the BMW M3 Evolution convertible that David Beckham (in the words of the catalogue) “used to court Posh Spice”. Even though the couple are the most famous in show business, it fetched £15,250, which is only about 10% over the usual market value for the car.

So who’s going to be hot in the future? Experts advise Rod Stewart, whose Lamborghini Miura complete with kinky stiletto dents in the roof went for £78,900 last year, and Elton John are ones to watch.

“Predicting who’ll be a big earner when they’re gone involves a massive amount of crystal ball gazing,” says Schofield. “Ultimately a car’s worth is relative to one thing — how badly someone wants it.”