Mid Bedfordshire MP Nadine Dorries has been accused of spreading "fake news" after sharing a video on social media suggesting Sir Keir Starmer had been reluctant to prosecute grooming gangs when he was director of public prosecutions.
Ms Dorries, who is a health minister, re-tweeted the clip of an interview with the Labour leader in which he appeared to be listing a series of reasons for not bringing charges - including if the alleged victims had been in trouble with the police - with the comment "revealing".
But Labour said the video had clearly been "doctored" and that he was actually explaining the flaws in previous guidance to prosecutors which he had withdrawn and replaced.
Downing Street said the minister had been "spoken to" by the GovernmentWhips' office to remind her of the need to check claims on social media before repeating them.
In response to the post by Ms Dorries, MP for Mid Bedfordshire, Labour's Wes Streeting replied: "What's revealing is that: 1. You've spread fake news and indulged a smear being promoted by the far right. 2. You had time to do this despite being a minister in the Department of Health during a public health crisis.
"It's either malevolence or stupidity. Probably both."
The former senior prosecutor Nazir Afzal, who was involved in bringing a number of cases, said the clip was being used to suggest Sir Keir did not take child sexual abuse seriously, when the opposite was true.
"As national lead, I can assure you that he and I put right the failings of a generation of those who should have safeguarded children. He inherited failure and left success," he tweeted.
A Labour Party source said: "This is a doctored video tweeted by a far-right social media account.
"As a Government minister, we hope Nadine Dorries acknowledges this and takes it down."
Following the furore, the posting appeared to have been deleted from Ms Dorries's timeline.
Two other Conservative MPs - Maria Caulfield and Lucy Allan - were also reported to have re-tweeted the same posting only to have subsequently deleted it.
A Downing Street spokesman said: "These tweets have rightly been deleted.
"The MPs involved have been spoken to by the whips' office and reminded of their responsibility to check the validity of information before they post on social media sites."
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