Boris Johnson has sparked outrage after claiming money spent investigating historic child sexual abuse had been “spaffed up the wall”.

Labour branded the ex-foreign secretary a “shameless, dangerous oaf” for his latest gaffe, which came in response to questions about police numbers during a radio phone-in.

Mr Johnson, who has long harboured Tory leadership ambitions, argued that money spent on investigating historic crimes would be better channelled into boosting police numbers, in the wake of a spate of fatal stabbings.

But the former London mayor’s crude choice of language immediately drew criticism, with MPs urging him to apologise to victims.

Mr Johnson told LBC: “Keeping numbers high on the streets is certainly important but the question is about where you spend the money and where you deploy the officers.

“And one comment I would make is I think an awful lot of money and an awful lot of police time now goes into these historic offences and all this malarkey.

“You know, £60m I saw was being spaffed up a wall, you know, on some investigation into historic child abuse.

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“What on earth is that going to do to protect the public now?”

Shadow policing minister Louise Haigh said his comments were inappropriate and offensive to victims’ families, branding him a “shameless, dangerous oaf”.

She added: “Could you look the victims in the eye and tell them investigating and bringing to justice those who abused them, as children, is a waste of money?”

Nazir Afzal, a former chief crown prosecutor in northwest England who led prosecutions into abuse in Rotherham, condemned the remarks.

He tweeted: “Tell that to those whose lives were devastated by abusers. Tell that Frances Andrade [a musician who accused a former choirmaster of abuse] who took her own life 30 yrs after the abuse she lived with every day.”

Angela Rayner, the shadow education secretary, said: “Boris Johnson hits a new low even for him, disgusting comments and he must apologise for his remarks.

“This self-serving individual makes a career out of gaffes but this is truly awful stuff.”

Ministers established the Independent Inquiry into Child Sexual Abuse (IICSA) in 2014 in the wake of allegations of abuse by Jimmy Savile.

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The inquiry has heard evidence of horrific abuse linked to children’s homes, schools, the Catholic and Anglican churches and government migration programmes.

Mr Johnson committed a string of humiliating gaffes while foreign secretary, which included reciting a colonial poem in a Myanmar temple and referring to the continent of Africa as “that country”.