Customers looking for a used Ford or Vauxhall are currently facing an odd fluctuation in depreciation values.

According to EurotaxGlass’s, the latest-generation Ford Focus and Vauxhall Astra are depreciating at a much slower rate than their siblings in the sector above - the Ford Mondeo and Vauxhall Vectra.

When age, specification and mileage are comparable, the smaller car from the same manufacturer will have a used retail price up to £1,500 higher.

For example, a 2005 05-plate Ford Focus 2.0 Zetec five-door with 8,000 miles on the odometer would this month typically have a retail price of £11,900, compared to £10,550 for a 2005 05-plate Ford Mondeo 2.0 Zetec five-door with identical mileage.

There is a similar story with the equivalent Vauxhall models. For example, a 2005 ’05-plate Vauxhall Astra 1.6 Club five-door (after 8,000 miles) currently has a retail price of around £10,100, whereas a 2005 ’05-plate Vauxhall Vectra 1.8 Club five-door can be found for £9,600, despite it having a more powerful engine and being the bigger car.

EurotaxGlass’s said the misalignment of residual values occurs largely because the Focus and Astra have been launched more recently, and the availability of used examples is low relative to current retail demand. By contrast, the Mondeo and Vectra are a later stage in their planned lifecycle and, as a consequence, demand has eased back and supply is now comparatively plentiful.

“As availability steadily improves, we can expect to see values for the Focus and Astra fall back,” said Adrian Rushmore, managing editor at EurotaxGlass’s. “The honeymoon for the latest Astra may be nearing its end, with the used retail price premium over the Vectra having fallen consistently during the past 12 months.

“The values of volume-brand upper-medium cars have been improving slowly over the past year, largely as a result of the higher number of diesels entering the used car market at prices significantly higher than their petrol counterparts.

However, the comparatively greater popularity and stronger residual value performance of vehicles in the lower-medium sector means cars such as the Mondeo and Vectra will continue to represent impressive value for money for the used car buyer for the foreseeable future,” he added.