Sir Keir Starmer nominated a former adviser for a peerage despite him having previously campaigned for a councillor charged with child sex offences.
Earlier this month, Downing Street announced that Matthew Doyle, who served as No 10 director of communications before stepping down in March, had been nominated for a peerage by the prime minister.
Downing Street has now admitted that Mr Doyle’s links with Sean Morton were “thoroughly investigated” before he was nominated for a peerage, with several interviews taking place with Mr Doyle himself.
It is understood that No 10 was satisfied that a past acquaintance did not represent a bar to Mr Doyle’s appointment to the Lords.
Morton, who was the Scottish Labour councillor for Fochabers and Lhanbryde, was charged with possessing and distributing indecent images of children in December 2016 and was later convicted in February 2018 of crimes including possession of several pictures of naked girls as young as 10.
Morton was suspended by Labour after appearing in court, but Mr Doyle is reported to have campaigned for him when he sought re-election as an independent councillor in May 2017.
Pictures seen by The Sunday Times show Mr Doyle wearing a T-shirt reading “Re-elect Sean Morton”. The newspaper also reported that he accompanied Morton to the election count.
In a statement to the newspaper, Mr Doyle said: “Sean Morton was maintaining his innocence at this time. I regret supporting him.
“Sean Morton was someone I knew for a period through other shared acquaintances. I have not seen him for years.”
Morton was given a community payback order, which included 140 hours of unpaid work within nine months. He also received a three-year supervision order and was placed on the sex offenders register.
It comes just weeks after Scottish Labour MSP Pam Duncan-Glancy announced she would not seek re-election to Holyrood over links to Morton.
Mr Duncan-Glancy stood down as the party’s education spokesperson after admitting she made a “serious error of judgement” over her links to the sex offender.
She said: “While this has obviously been a very difficult decision – and it is the greatest honour of my life to represent Glasgow – I do not wish for a personal friendship to become a distraction.
“I am grateful to have had the opportunity to serve, and I remain committed to returning a Scottish Labour government next year.”
A Downing Street spokesperson said: “Questions regarding Matthew Doyle’s past acquaintance with Sean Morton were thoroughly investigated, including through several interviews with Matthew Doyle, prior to his appointment.”
Mr Doyle and Morton have been contacted for comment.