The world's most extravagant car extras

Bentley buyers have the option of this diamond-encrusted clock
Bentley buyers have the option of this diamond-encrusted clock

A personalised numberplate is a very visible way of making your car just a little bit special.

And while prices can go as high as tens of thousands of pounds, personal plates can actually be surprisingly cheap.

That's not the case, though, with some other added extras.

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"Targeting a market with more disposable income to burn allows car manufacturers to slip in pricier choices," explains a spokesperson for personalised numberplate dealer Regtransfers.

"Some are very tasteful. Take for example the Rolls-Royce's magnificent 'starlight' headliner option. Over 800 fibre optic lights woven into the roof of your vehicle, in a celestial pattern or a custom design of your choosing. We're struggling to see how this option would benefit a Ford Ka, but when it comes to a Rolls, expense is rarely an issue."

Other added extras are even more extravagant: here are some of the best.

Of course, there's no reason why you can't just use an ordinary coat hanger hooked to the back of the seat - unless you're a label-minded Jaguar owner, that is. If you want one carrying the Jaguar logo, you can have one - at a cost of £46.

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Air freshener
You can't expect owners of the Mercedes-Benz E550 Coupe to hang a pine-scented bit of cardboard from the mirror. But for just £360, they can have a 'scent system' with a range of controllable smells. Our favourite has to be Downtown Mood - a 'transparent floweriness with a subtle metal effect'.

Fancy trim
It's become a must-have for kitchens - and now Mercedes-Benz Maybach drivers can have it in their car too. The Granite Trim Interior adds £2,310 to the cost of the car.

Car key
If you drive an Aston Martin, you're far too sexy to fiddle around with an ordinary key. But for a mere £22,904 to £35,522, you can buy a special watch that can unlock your car for you. Alternatively, of course, you could just pay a chauffeur.

Metallic paint
A metallic finish generally costs a little more than a standard paint job - but £50,631 more? Well, that's what it costs buyers of the Porsche 918 Spyder if they fancy Liquid Metal silver or blue paint. Just make sure you don't scratch it.

Dashboard clock
It's useful to know the time when you're driving, even if you're the owner of a Bentley Bentyaga without a care in the world. And if only a diamond-encrusted model will do, you'll presumably be perfectly happy to fork out an extra £150,000.

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Leather seats...

Most people would agree that leather seats add a bit of luxury to any car. But are they worth as much as a new car itself? The Design Selection seats for the Audi A8 cost an extraordinary £12,365 extra.

...and more leather seats
For some car buyers, even that's not enough. At one stage, the Dartz Prombron Monaco Red Diamond Edition SUV was available with seats made from whale penis leather - until Greenpeace and the World Wildlife Fund took exception. The option was eventually withdrawn.