The party began a controversial campaign last week in which they accused the prime minister of failing to send child sex abusers to prison, being soft on gun crime and suggesting thieves should not be punished.

Their latest advert appeared to refer to Mr Sunak's wife, Akshata Murty, who previously benefitted from non-domicile tax status in the UK.

In his first public comments on the adverts, Sir Keir said on Wednesday: "I make no apologies for highlighting the failures of this government.

"They've broken our NHS, they've broken our economy.

"And this argument that because they've changed prime minister five times, that somehow the prime minister doesn't bear responsibility for 13 years of grief for many, many people, I just don't think stacks up."

Pressed on the latest ad, he said: "Nobody is targeting the prime minister's wife.

"Behind these adverts is a basic truth - that they have broken our criminal justice system, broken our NHS, and broken our economy."

Sir Keir joins a lineup of leading Labour politicians who have defended the ad campaign, and marks a change in his normal "nice guy" persona.

On Tuesday, shadow chancellor Rachel Reeves said she was "not going to make any apologies" for the ad campaign the party has launched in recent days, which critics have branded "gutter politics".

"I back these ads because they are highlighting the dire record of this Conservative government," she said.

Mr Sunak sought to dismiss the attack ads, telling reporters on Wednesday: "I said at the beginning of this year I was focused on delivering for the British people.

"There were five things I said I wanted to do, which was to halve inflation, grow the economy, reduce debt, cut waiting lists and stop the boats.

"And that's what I'm focused on, day in day out, delivering for people."

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He added the British people want "less talk, more action" from their politicians.

A Conservative source told Sky News on Tuesday the latest attack ad involving Ms Murty was "the height of hypocrisy from a party which has already made £90bn of unfunded spending commitments".

The campaign also received criticism from Liberal Democrat leader Sir Ed Davey, who said: "I think it's wrong when people attack individuals personally, particularly over subjects which are so sensitive, which are so important to the British people."