Folding hard-top sales now represent 5.2% of the whole UK market, according to Glass’s Guide.

Published by EurotaxGlass's, the guide says one by-product of the rapid rise of cars with a folding hard-top – often referred to as coupe-cabriolets or 'CCs' - is that convertible sales are slowly becoming less concentrated around the summer months.

Despite the increase in availability of convertibles now entering the used car market, there is no evidence of any weakening in residual values relative to other sectors.

The average volume-brand convertible holds on to 52% of its original list price after three years and 36,000 miles, compared to 59% for a premium brand convertible. This compares very favourably with the 45% retained value for the average used car across the market as a whole.

While all three figures are down compared to this point last year, the relative differences between the three categories are unchanged, demonstrating the continued strength of convertibles in the used market. It is, however, apparent that the residual values of CCs are starting to outperform those of conventional soft-tops.

"Over the next two years we expect to see values of three-year-old soft tops from the volume brands lose ground to the CCs," says EurotaxGlass’s Adrian Rushmore.