Efforts to deter the use of diesel cars in London appear to have failed, with their share of the market reaching a record high in 2015, according to Leonie Cooper, Labour’s London assembly environment spokesperson, who obtained the figures from the Department for Transport.

With diesel vehicles being blamed for causing high levels of pollution in the capital, Sadiq Khan, the new mayor of London, has been lobbying for a diesel scrappage scheme, a policy that was backed by his predecessor, Boris Johnson.

The number of diesel cars licensed in London rose from 601,456 in 2012 to 774,513 in 2015, an increase of nearly 29%. The number of petrol vehicles fell over the same period, from 1,901,127 to 1,797,099, leaving diesel with a record high percentage of the market, at 29.4%.

“Government can no longer turn a blind eye to the serious consequences of diesel emissions,” said Cooper. “This worrying rise in diesel engines shows that they are running out of opportunities to bat away calls for a scrappage scheme.”

Khan’s first major policy announcement was to say he would double the size of a planned clean air zone in London, and bring it in a year earlier than planned.

This week he added that he would like new powers to set vehicle excise duty, which has been blamed by campaigners for incentivising the switch to diesel.

“VED (vehicle excise duty) collected from London registered vehicles could be devolved, allowing the mayor to set the rates and determine how the income raised is spent. If VED was devolved, it would be possible to restructure the way it is levied so as to tackle air quality by incentivising cleaner vehicles and investing VED revenue into air quality measures,” said a submission by the mayor to a court case being brought against the government over its clean air plans.

A spokeswoman for the mayor said: “Cleaning up London’s toxic air will be impossible without urgent government action. National policies caused the dieselisation of the vehicle fleet so it is only right government now sort out the consequences.

“Implementing a national diesel scrappage scheme is something that should have been addressed years ago and would quickly reduce the number of polluting vehicles driving throughout the capital every day.”

Last week transport minister Patrick McLoughlin suggested the Chancellor would have to look at increasing taxes on diesels to discourage people from buying them.

A public consultation will take place this summer on his new measures to tackle air pollution in London.