The London Labour party is considering making a formal complaint to the BBC and the head of the civil service about Boris Johnson’s verbal attack on Sadiq Khan during a Government press conference on coronavirus.

Mr Johnson accused Mr Khan of “blowing” Transport for London’s (TfL) finances through an “irresponsible fares policy” after he had left them in “robust good order”.

The comments – made on Monday at a televised coronavirus press conference at Downing Street’s £2.6 million media briefing room – were said during the pre-election purdah for the London mayoral election on May 6.

The purdah period places limits on government publicity around the election.

The restrictions, outlined in the Local Government Act 1986, ban government officials from publishing “any material which, in whole or in part, appears to be designed to affect public support for a political party”.

London Labour said on Tuesday that Mr Johnson’s comments about Mr Khan breached these regulations and it is considering writing a formal letter of complaint to the BBC and Cabinet Secretary Simon Case, who is also head of the civil service.

Mr Khan is standing for a second term as mayor of London as the Labour candidate.

Launching his mayoral manifesto at a play centre in north London, Mr Khan accused the Conservative leader of using his Government platform to “tell lies”.

He told the PA news agency: “If he’s (Boris Johnson) going to use a Government platform to talk politick, he should at least tell the truth.

“It is a fact that when I became mayor the TfL’s deficit was more than £1.5 billion. I reduced it by more than 71% before the pandemic. But also he increased TfL’s debt by more than £7 billion.

“I think it is inappropriate for all of us to follow the rules and abide by the rules, and Boris Johnson to yet again break the rules in the way he’s done.

“Firstly, during the purdah period using a Government platform to attack a Labour candidate. But secondly, to tell lies.”

Asked at Monday’s press conference about potential Government support for London’s pandemic recovery, the Prime Minister said: “As for the finances of TfL, I must respectfully remind you that I left them in robust good order and it is not through any fault of my own that the current Labour mayor decided to blow them on an irresponsible fares policy.

“We’re doing our best to help them out and will continue to do so. But I’m afraid you’ve got to look at some of the decisions that were taken by the current Labour mayor as well.”

In his manifesto,  Mr Khan says he wants to build a “greener, fairer, safer and more prosperous city”.

If elected, he aims to avoid “a 1980s-type recession” by implementing a Green New Deal that “gives Londoners the skills they need for future-proof jobs in the green sector” such as in solar, electrified buses and retrofitting homes to be more energy efficient.

At the launch event, Mr Khan stood by his commitment to launch a drugs commission which would investigate the merits of decriminalising cannabis, despite Labour leader Sir Keir Starmer telling Sky News that current drug laws are “roughly right”.

Mr Khan said he would commission a cross-section of experts to look into the issue of decriminalising the drug, but would not “pre-judge the outcome”.

“I’ve seen for myself the impact of violent crime linked with drugs. I’ve seen for myself the impact on health because of cannabis but I’ve got an open mind.”