Labour is defying its critics by continuing to publish advertisements attacking the Tories despite a backlash even from one of its own MPs.

On Friday, a fresh post on Twitter suggested the Conservative Party is weak on firearms offences.

Using the same format as the heavily-criticised first poster, it asks: “Do you think an adult convicted of possessing a gun with intent to harm should go to prison?”

Before answering, “Rishi Sunak doesn’t”, and adding Sunak’s signature.

It includes the statistic: “Under the Tories 937 adults convicted of possession of a firearm with intent to harm served no prison time. Labour will lock up dangerous gunmen.”

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.

The first poster – which was variously described as “gutter politics”, “idiotic” and “a new low in British political attack ads” – suggested Sunak did not support the jailing of child sex offenders.

The tweet has come in for a wave of criticism from across the political spectrum, including from former Labour shadow chancellor John McDonnell, who said: “We are better than this.”

In an excruciating interview on BBC Breakfast this morning, shadow culture secretary Lucy Powell repeatedly refused to say she personally supported the tweet.

HuffPost UK has reported the party was planning to step up its attacks – despite the furore – after holding talks with political allies in America and Australia over how to take the fight to the Conservatives in the run-up to the next election.

Labour was accused of a “vile and desperate” campaign strategy by Tory deputy chairman Lee Anderson and “cheapened and debased” politics by SNP MP John Nicolson after posting the advert on Twitter.