Car retailers increased their stock of used cars by an average of 15% in May but took longer to sell vehicles according to analysis of year-to-year trends analysed by Motors.co.uk.

Forecourt stock levels rose from 60 during May 2018 to 69 last month as days to sell increased from 38 to 40 days, it said in its latest Market View report.

The fastest average sales in May were achieved by car supermarkets, which took an average 28 days, the same as 12 months ago and one day faster than April.

Dermot Kelleher, Motors.co.uk’s head of marketing and business intelligence, said: “Our Market View shows how franchised and independent dealers worked hard in May to source desirable stock.

“We know many businesses are extending company car replacement cycles until they know how the WLTP (Worldwide Harmonised Light Vehicle Test Procedure) emission rules will impact the benefit-in-kind tax regime and this continues to put pressure on supply.

“We expect competition for ready to retail stock to remain fierce over the coming months.”

Over the course of May Motors.co.uk found that franchised dealers carried more stock than their independent counterparts, averaging 65 cars per site compared with 51 cars on non-franchised sites.

Year-on-year stock levels also increased for both with independents finding forecourt space for an additional eight cars, compared with four more on franchised sites.

The fastest selling used cars in May were EVs, averaging just 37 days to sell, compared with 47 days in May 2018, followed by petrol (38 days), hybrids (39 days) and diesel (41 days).

Although petrol is the consumer fuel of choice, demand for used diesel cars continued to hold up in May.

Diesels accounted for 45.5% of online views, compared with 47.1% 12 months ago, while petrol rose slightly year on year from 51.6% to 52.6%.

Diesel accounted for 47.1% of dealer stock, down from 50.2% a year ago, while petrol increased from 48.5% to 51.3%.

The fastest selling used car in May was the Vauxhall Vectra according to Motors.co.uk’s data, averaging 24 days on dealer forecourts, followed by the Vauxhall Antara and Hyundai Tucson both taking 28 days and the Suzuki Alto and Volvo V60 both on 29 days.