Rishi Sunak’s decision not to address calls for an investigation into reports of Conservative-run Facebook groups engaging in “gutter politics” is an “abject failure of leadership”, Labour has claimed.

The Prime Minister faced calls to condemn the groups and launch a probe into reports that Tory candidate for London mayor, Susan Hall, is a member of them.

The Observer newspaper reported over the weekend that Ms Hall is a member of a Facebook group said to contain Islamophobic speech and threats to incumbent Labour Mayor of London Sadiq Khan.

Mr Sunak was asked about such groups and their links to Conservative campaigners twice during Prime Minister’s Questions, taking place on the eve of local elections across England and Wales.

He insisted that his party was campaigning “on the substance of the issues that Londoners face”.

The Conservative Party has meanwhile said it is reviewing its policies regarding Facebook groups.

Speaking after PMQs, a Labour spokesman told reporters: “I think it is bizarre that the Prime Minister couldn’t speak out and say that these things are inappropriate.

“We know that the Government dragged its feet when it came to producing the online harms bill (Online Safety Act), and across the board it just isn’t taking the influence that these groups have seriously enough.

“We would urge the Tories to clamp down on this sort of activity.”

They added: “To me, I think I would describe it as an abject failure of leadership.”

In the Commons, Labour MP Catherine West (Hornsey and Wood Green) had asked: “It has been revealed by the Observer newspaper that the Conservative candidate for the mayor of London is actually a member of the six Facebook groups which was mentioned by the member for Edinburgh North.

“They are full of Islamophobia, antisemitism and the most disgraceful incitement to damaging property and the worst bit, for those of us who were in the House when our Members of Parliament were taken, death threats to the current Mayor of London, Mr Khan.

“Will he close down these Facebooks which have been begun by Conservative members of staff, and will he investigate the role of the current candidate and her membership of those disgraceful racist Facebooks?”

Mr Sunak replied: “The election tomorrow will be fought on the substance of the issues that Londoners face and the Labour record is crystal clear. Housebuilding in London has collapsed, knife crime is rising, mayoral taxes are up 70% and drivers have been hit with Ulez (ultra low emissions zone) charges, and the Labour mayor just simply panders to unions, and has decimated London’s night-time economy.

“That is his record, that his how he will be judged and people across London know that they will be safer with the Conservatives, with lower taxes and better services.”

SNP MP for Edinburgh North, Deidre Brock, had earlier said: “Can the Prime Minister shed some light on these shady groups spreading abuse, their funding, their links to his party, and whether he is aware of similar operations existing elsewhere in the UK?

“If he won’t, will he at least commit today to investigate and take action to tackle the sources of this grubby gutter politics?”

The Prime Minister responded: “I am not aware about the topic that she raises, but I am not going to make any apology for Conservatives pointing out the record of whether it is the SNP in Scotland or the Labour Government in Wales, because that is exactly what democratic process is about.”

A Conservative Party spokesperson said: “The Conservative Party unequivocally condemns all discriminatory language, and never encourages nor condones vandalism or criminal activity.

“The Conservative Party is reviewing its processes and policies regarding Facebook groups.”