Volkswagen’s UK boss is predicting diesel’s share of the UK car market could drop to as low as 30% as sales of petrol and alternative-fuelled cars strengthen.

“The percentage of diesel will decline. It’s already happening. The first to be affected will be small cars,” said VW Group UK boss Paul Willis, speaking at the Future of the Car Summit organised by the Financial Times.

Willis, who didn’t give a timescale for the reduction, said a 30% share was his lowest estimate and it “maybe” will remain as high as 40%.

Diesel has steadily gained at the expense of petrol since the turn of the century. In 2000 10% of cars in the UK were diesel and it currently holds just over half the market. Sales of diesel fuel have also grown steadily while petrol has declined with annual sales of 17bn litres of petrol versus 18bn litres of diesel, with an additional 10bn litres of diesel in the commercial sector.

However this trend appears to have halted. In 2015 petrol registrations were up 8.4% compared to diesel’s 3% and they both had a 48.5% share of the new vehicle registrations.

A number of factors have influenced the change. Diesel was considered more economical than petrol, but more efficient petrol engines are closing the gap, and concerns about pollution and more recently the Dieselgate affair have made diesel less attractive.

However, Willis said the decline would be halted by new, clean diesel engine designs which would alleviate environmental concerns.