The values of used prestige-badge luxury cars (such as the BMW 7 Series, Mercedes S-class and Audi A8) in the UK now fall significantly short of the market average if a vehicle is not fitted with satellite navigation system.

According to used car price guide firm Glass's Information Services, prospective buyers of luxury used cars will typically now either walk away if a vehicle lacks satellite navigation, or will instead expect up to £2,500 to be taken off the asking price in the case of vehicles up to two years old.

"Satellite navigation should no longer be viewed as an expensive indulgence for prospective buyers of new luxury cars," said spokesman Richard Crosthwaite. "It has become a crucial investment, underpinning the future residual value of the vehicle. Our analysis of the market demonstrates that the initial outlay will be more than recovered when it comes to sell the car to its next owner.

"This technology is now a standard feature throughout the Mercedes S-class range, but it remains an option on many other vehicles in the class and buyers should not hesitate to tick the 'sat-nav' box on the options list."

Glass's predicts that within two years, satellite navigation systems will become similarly crucial for owners looking to achieve the typical market value for a smaller used prestige badge vehicle, such as a BMW 5 series or Mercedes E-class.

"As sat-nav systems become prevalent, used car buyers will increasingly expect to see such systems appear on more premium-badged cars. This is already happening with larger-capacity engine models in this sector and with prestige sports utility vehicles, where securing the optimum market value is steadily becoming more dependent upon the inclusion of sat-nav."