Like a unique piece of china, rare coin, or one-of-a-kind ornament, well-preserved collectible cars can be worth a small fortune if you wrap them in cotton wool and barely drive them.

However,  a Jaguar being sold at auction next month has proved that sticking a potential future classic in storage for 28 years can backfire.

The model in question is a 1990 XJS V12 HE that’s covered just 840 miles from new and remains almost in the same condition it was when it left the factory almost three decade ago.

So you might assume it is worth a fair whack by today’s standards? However, it’s only valued at half the price the first owner would have paid for it.

It highlights that if you do the sums and adjust for inflation, stashing a car away is not always a sure fire investment.

Delivered by the Bristol Motor Company to the first owner on the 19th May 1990, Silverstone Auctions has described the timewarp Jaguar XJS HE Automatic as a ‘rare find indeed’.

It is offering the coupe at a UK auction next month with an estimate in the region of £35,000 to £40,000.

Hagerty Classic Insurance values a concours-condition XJS V12 HE at £13,500 today, while a shabbier example will only set you back around £3,900. That means the estimate for this almost unused one is a significant premium.

But while that might sound like lot of money, it’s almost exactly the same price it was when it originally rolled off the production line almost three decades ago.

That’s because the list price of this car in 1990, according to Jaguar Classics, was £34,200.

Even allowing for it selling at the top end of the estimate, with the hammer going down at £40,000, with the impact of inflation taken into account this untouched gem has halved in value.

Despite having barely been used in a conscious effort to safeguard it, the higher estimate is less than half the inflation-adjusted original price, which works out at £81,014 – according to This is Money’s inflation calculator.

This will be music to the ears of enthusiasts and traditionalists among the classic car world who might not agree with the idea of shoving unused vehicles into storage to profit from potential future values, instead of driving and enjoying them.

Silverstone Auctions, who is selling the preserved Jaguar XJS, said it still has a hint of that new-car smell despite being 28 years old

As you can see, the engine bay is almost as clean as it was when the car left the production line. Unfortunately – for the seller – the efforts to preserve it haven’t made them a profit.

The mint condition Jaguar is still expected to draw plenty of attention, as not too many opportunities will arise in the future to own one that’s barely turned a wheel in almost three decades.

There’s barely a hint of wear and tear on the burgundy metallic paint and no signs of tugs or splits in the cream leather interior.

Even the mahogany dashboard, centre console panels and door inserts have the fresh glossy coat of lacquer it was first graced with.

Silverstone Auctions even claims it ‘even retains some of that distinctive new car smell’.

Under the bonnet, the 5.3-litre V12 engine is spotless and should retain all 299bhp it left the factory with.

The first owner took delivery in 1990 and kept it in storage for the next 25 years.

The current vendor bought the vehicle in 2015 and has barely put a mile on the classy British coupe since.

All the original books, manuals and service documentation is present along with some previous MOT forms.

The auction takes place at Silverstone race circuit in Northamptonshire on 21 and 22 July.

It will be offered to the highest bidder alongside a 1987 Ford Sierra RS500 Cosworth with 10,840 miles on the clock that’s predicted to sell for a more impressive £105,000.

Some 21 years ago, the fast Ford would have cost £19,950 new.

That works out an inflation-adjusted £55,685, so the Sierra Cosworth at least is almost twice as valuable today as it was when first sold.