With so much information to digest, compilers of used car valuations must have moments when they want to reach for the Rennies. CAP’s chief editor Chris Crow says that for starters there are around 50,000 makes of model and their derivatives.

“Add their different ages and mileages and you’re probably looking at a million bits of data.”

Other ingredients going into the mix include condition, non-standard features, any tweaks needed to take into account seasonal and regional variations, along with what’s in and out of fashion – all of which have to be processed and served up in a menu palatable enough for dealers to pay for.

One of the most challenging out of this list is optional spec.

As Jeff Paterson, chief car editor at Glass’s, joked: “One man’s choice of leopard skin seats is not to everyone’s taste.”

What can be predicted with confidence is that non-standard features lose their factory-fresh value as rapidly as the cars themselves.

Bad news for buyers of new cars seduced by the option list, but better news for dealers at trade-in time.

As Chris Green, dealer principal at Sky Ford in Hemel Hempstead, put it: “You may have to pay slightly more for the higher-specced (used cars), but they are more saleable than a load of standard stock which everyone else has got.”

Green’s sales manager Ryan Smith added: “Leather seats are a good selling feature on people carriers because they’re used by families and are easier to keep clean.

"Panoramic roofs hold appeal on larger people carriers, and buyers of larger saloons tend to want bigger alloys.”

According to Paul Wright, director of AM Award-winning Eddie Wright’s used car supermarket in Scunthorpe, sat-nav, leather, panoramic roof, upgraded alloys and rear media systems are popular, with white and black – and on certain vehicles, yellow – being the current ‘hot’ colours.

Kieren Puffett, editor of Parkers, reports: “Factory-fitted options that add value obviously vary from sector to sector.

"For instance, leather on compact execs will add value, but on premium execs it is expected as standard, so if a car doesn’t have it, it will lose value.

"Minis without TLC packs will be worth less because so many new Minis are sold with them.”

The wrong colour and insufficient spec on premium cars can lose £500 to £1,000, according to Daren Wiseman, formerly with CAP and now general manager of valuation services with Manheim Remarketing.

“Off a manufacturer’s list of options, between 10 and 20 can enhance value at disposal time. Colour – white, black, or silver is all-important – something generally acknowledged by fleets, but not so with many private buyers, judging by some of the colours you see around.

"Current good sellers include Audi A3s with leather, sat nav and upgraded alloys.”