He on Tuesday accused Mr Johnson of thinking “the rules apply to anyone but him”, as he criticised the Government over reports of lockdown-breaking parties last year.

“I have heard so many heartbreaking stories of people who missed family funerals because they were abiding by the rules,” he said. “Meanwhile, the Prime Minister was at a cheese and wine party in Downing Street.”

In an apparent jibe at Mr Johnson, he said politics was not “a branch of the entertainment industry” but “the serious business of getting things done”.

Speaking to voters in “Red Wall” seats that abandoned Labour at the last election, Sir Keir said: “Take another look at Labour. We’ve changed. This Government is clearly not up to the job and we are offering solutions for the future that we want to discuss with you.”

A plan to scrap arrests for young people caught with cannabis in London may face opposition from Sadiq Khan’s own party, the Labour leader suggested.

Responding to a Telegraph report that the capital’s Mayor planned to offer under-25s speeding awareness-style courses rather than prosecution, Sir Keir said he would oppose any attempt to decriminalise drugs.

“I haven’t seen the detail of the proposals that you’ve reported on,” he said. As I understand it they are early measures, they are some sort of pilot. Obviously we’ll look at those, but I’m very clear that we’re not in favour of changing the drugs laws.”

On Tuesday, Mr Khan’s office said the pilot had not yet been signed off by City Hall and that he did not have the power to change drug laws but supported attempts to divert young drug users from the criminal justice system.