MPs and commentators from across the political spectrum have criticised a Labour attack ad claiming that Rishi Sunak does not think child sex abusers should go to prison.

The party was accused of “cheapened and debased” politics and “stooping low” after posting the advert on Twitter on Thursday.

In a tweet pitching itself as “the party of law and order”, Labour shared a photo of the Prime Minister smiling alongside the words: “Do you think adults convicted of sexually assaulting children should go to prison? Rishi Sunak doesn’t.”

SNP MP John Nicolson said: “This is absolutely nauseating. Politics cheapened and debased. The Labour Party wants to win, of course, but like this?”

Meanwhile former shadow chancellor and Labour backbencher John McDonnell urged the party to climb down, saying: “This is not the sort of politics a Labour Party, confident of its own values and preparing to govern, should be engaged in.

“I say to the people who have taken the decision to publish this ad, please withdraw it. We, the Labour Party, are better than this.”

Judges and magistrates, rather than the prime minister of the day, are responsible for handing out sentences and the figures Labour highlighted cover the period since 2010 – Sunak only entered Parliament in 2015 and did not become Prime Minister until October last year.

On Friday morning, a shadow cabinet minister refused to endorse the ad.

Shadow culture secretary Lucy Powell (below) declined to say she stood by the social media message, but insisted it was part of the “cut and thrust” of political debate which sought to highlight the Tories’ record on law and order.

The National: Shadow culture secretary Lucy Powell has said the employment of serving MPs as presenters on different media channels is ‘very concerning’ (Stefan Rousseau/PA)

On BBC Breakfast,  Powell suggested it was a “skit” based on Sunak’s own promotional material as she declined to say she stood by the tweet.

She said: “What I stand by is what that graphic is trying to show, which is that the Prime Minister of our country is responsible for the criminal justice system of our country and currently that criminal justice system is not working.”

Asked again whether she stood by the message, she said: “I stand by what this tweet and this campaign is trying to highlight.”

She added: “The graphic itself, obviously, is a skit based on his own graphics that he extensively uses.”

In response to McDonnell’s criticism, she added: “I can see that it’s not to everybody’s taste, absolutely, and that some people won’t like it.

“Clearly, John McDonnell is one of those.

“But that is the cut and thrust nature of politics.

“I didn’t design the graphic, it’s not my graphic.”

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The Twitter post, which highlights Labour analysis of Ministry of Justice data, said: “Under the Tories, 4Pauline McNeill called ‘transphobic’ over Nike boycott tweet500 adults convicted of sexually assaulting children under-16 served no prison time. Labour will lock up dangerous child abusers.”

Powell told Sky News: “We do have serious criminals now in this country almost routinely getting more lenient custodial sentences than they would otherwise do because the system is creaking at the knees.”

She said it was not down to sentencing guidelines but was due to “capacity in the system to actually implement those guidelines” with a “huge backlog” in court cases and pressure on prison places.

Asked if the Twitter post should be removed, she told Times Radio: “I don’t think it should be deleted.”

The National:

Law and order is a key political battleground as both parties compete for votes ahead of May’s local elections.

A Tory source said: “Labour HQ have highlighted Sir Keir’s appalling record at keeping children safe.

“During Sir Keir’s controversial tenure as director of public prosecutions, less than 30% of child pornographers saw the inside of a prison cell.

“It’s no wonder only 12% of his staff thought he was any good and criminals want a Labour government.”