An adviser to British Prime Minister Boris Johnson has resigned amid fierce criticism of his past comments linking intelligence to race and suggesting contraception should be made compulsory to avoid "a permanent underclass".

Key points: Mr Sabisky was hired as part of a Downing Street appeal for "weirdos and misfits"

Mr Sabisky was hired as part of a Downing Street appeal for "weirdos and misfits" He has suggested black Americans have a lower IQ than white Americans

He has suggested black Americans have a lower IQ than white Americans The PM's spokesman refused to comment on the controversy

Andrew Sabisky said he was quitting because he had become "a distraction".

MPs from both the Opposition and the governing Conservatives had called on Mr Johnson to fire Mr Sabisky.

Mr Sabisky was hired to work in the Prime Minister's 10 Downing Street office after Mr Johnson's chief aide, Dominic Cummings, appealed for "weirdos and misfits with odd skills" to apply for government jobs.

According to an online biography, Mr Sabisky has a master's degree in the psychology of education.

In 2014, he wrote: "One way to get around the problems of unplanned pregnancies creating a permanent underclass would be to legally enforce universal uptake of long-term contraception at the onset of puberty. Vaccination laws give it a precedent, I would argue."

He has also suggested black Americans have a lower average IQ than white Americans.

His comments had been condemned by Mr Johnson's opponents, as well as some allies.

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Conservative MP Caroline Nokes, who chairs Parliament's Women and Equalities Committee, tweeted: "Cannot believe No 10 has refused to comment on Andrew Sabisky.

"I don't know him from a bar of soap, but don't think we'd get on … must be no place in government for the views he's expressed."

Scottish First Minister Nicola Sturgeon said Mr Johnson's Government needed "to get a grip fast and demonstrate some basic but fundamental values in the terms of our public debate".

On Twitter, Mr Sabisky, who has since deleted his account, accused critics of "selective quoting", saying, "I signed up to do real work, not be in the middle of a giant character assassination".

"The media hysteria about my old stuff online is mad but I wanted to help [the Government], not be a distraction. Accordingly, I've decided to resign as a contractor."

Earlier on Monday, a spokesman for Mr Johnson declined to discuss Mr Sabisky's role in Downing Street, saying: "I'm not going to be commenting on individual appointments."

Spokesman Jamie Davies also refused to say whether the Prime Minister agreed with Mr Sabisky's views, which critics said amounted to support for eugenics — the now-discredited movement to improve the human race through selective reproduction.

"The Prime Minister's views on a range of subjects are well publicised and documented," Mr Davies said.

Mr Johnson has his own record of offensive comments.

It's the latest controversy connected to Mr Cummings who helped mastermind the successful Vote Leave campaign. ( Reuters: Henry Nicholls )

He has called Papua New Guineans "cannibals," referred to people in Commonwealth countries with the offensive term "picaninnies" and said the children of single mothers were "ignorant, aggressive and illegitimate".

The episode is the latest controversy connected to Mr Cummings, a self-styled political disruptor who helped mastermind the successful Vote Leave campaign in Britain's 2016 European Union membership referendum.

Last month, Dominic Cummings put out a call on his blog for "super talented weirdos" to join the Government. ( Reuters: Simon Dawson )

He took up his powerful role as Downing Street adviser after Mr Johnson became Prime Minister in July.

Last month, Mr Cummings put out a call on his blog for "super talented weirdos" to join the Government and expand its roster of talent.

"We need some true wild cards, artists, people who never went to university and fought their way out of an appalling hell hole, weirdos," he wrote.

AP