Controversy over Downing Street aide Andrew Sabisky heightened today after the emergence of comments issued under his name which said there were “very real racial differences in intelligence”.

Downing Street has refused to say whether Boris Johnson agrees with previous comments in which Sabisky suggested black people were mentally inferior and advocated compulsory contraception to prevent a “permanent underclass”.

Asked repeatedly at a Westminster media briefing whether the prime minister would condemn or distance himself from his aide’s comments, a No 10 spokesman said only: “The prime minister’s views are well publicised and well documented.”

The failure to condemn Sabisky’s remarks was denounced as “disgusting” by Labour, while Scottish first minister Nicola Sturgeon said it was time for Downing Street to “demonstrate some basic but fundamental values”.

Mr Johnson was coming under intense pressure to sack the aide, apparently recruited by Dominic Cummings after he responded to the senior adviser’s appeal for “misfits and weirdos” to work at No 10.

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Acting Liberal Democrat leader Ed Davey said the government had become a “national embarrassment” and called on the PM to curb Cummings’ power to “appoint and sack at will”.

Conservative former immigration minister Caroline Nokes, who now chairs the Commons Women and Equalities Committee, said there was “no place in government” for the views expressed by Sabisky.

“Cannot believe No 10 has refused to comment on Andrew Sabisky,” tweeted Ms Nokes. “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.”

As the furore raged, Sky News uncovered further comments released under Mr Sabisky’s name and his Twitter avatar in 2014, suggesting that there may be “genetic reasons” for differences between the races in intelligence and that these should be taken into account when framing immigration policy.

“There are excellent reasons to think the very real racial differences in intelligence are significantly – even mostly – genetic in origin, though the degree is of course a very serious subject of scholarly debate,” the post stated.

“That debate busily bustles on and I’m sure we’ll have more precise answers in another five years or so, though whether the politicians will pay any attention is debatable.

“It would be nice if they did from the standpoint of immigration control – in the UK, that is.”

Meanwhile, a 2014 book review by Sabisky emerged in which he suggested that the UK’s constitution may have to be amended to respond to the likelihood that Britain would be a Muslim majority nation by 2050.

“Will institutionalised power-sharing (as in Northern Ireland) become the norm in the West – not between Catholic and Protestant, but between Muslim and non-Muslim (by around 2050 Britain is forecast to be a majority Islamic nation on current birthrate trends)?” he wrote. “How much internal resistance will there be to the adaptation of current institutions? How much of the resistance, and counter-resistance, will be violent?”

The No 10 spokesman was asked around 40 times about Mr Johnson’s opinions on Sabisky’s comments on eugenics and racial intelligence during a half-hour media briefing in Downing Street on Monday but declined to set them out.

Instead, the spokesman repeatedly read from a text stating that his views were “well-publicised and well-documented”.

Despite repeated requests, the Downing Street spokesman was unable to point to a single example of the prime minister expressing a view on eugenics or the intelligence of black people, merely saying that reporters would find that his opinions were “well-documented” on the public record.

He declined to say whether Mr Johnson’s views on the issue were reflected in a magazine article in which the PM referred to black people as “picaninnies” with “watermelon smiles”.

Whilst editor of The Spectator, Mr Johnson published an article in which columnist Taki ​Theodoracopulos wrote: “On average, Orientals are slower to mature, less randy, less fertile, and have larger brains and higher IQ scores. Blacks are at the other pole, and whites fall somewhere in the middle, although closer to the Orientals than the blacks.”

Asked subsequently about his contributor’s remarks, Mr Johnson described Theodoracopulos as a “very distinguished columnist”.

Calls have been made for Johnson to fire Sabisky​ (BBC)

Mr Johnson had already been coming under pressure to sack Sabisky over comments in which he:

- Called for the young to undergo compulsory contraception to prevent the creation of “a permanent underclass”;

- Disparagingly compared women’s sport to the Paralympics;

- Suggested that black people were more likely than whites to be “close to mental retardation”;

- Suggested that much of the ‘hue and cry’ against female genital mutilation ‘looks more like a moral panic’;

- Said that mental performance-enhancing drugs which might pose a risk to children’s lives were probably worth ‘a dead kid once a year’; and

- Made a case for eugenics as a means of “selecting ‘for’ good things” in the population.

Grant Shapps avoids answering questions on controversial comments made by Andrew Sabisky

The Downing Street spokesman refused to confirm his appointment or to say whether he was working as a special adviser to the PM paid by the taxpayer.

And he appeared to back away from the attempt by cabinet minister Grant Shapps to distance himself from Sabisky at the weekend when the transport secretary said that his reported comments were views that “neither I or the government share in any shape or form”.

Asked whether Mr Shapps was speaking on behalf of the government, the No 10 spokesman replied: “I didn’t hear specifically what the transport secretary said. The transport secretary was speaking as the transport secretary. I have answered the question on behalf of the prime minister.”

Labour party chairman Ian Lavery said: “It is disgusting that not only has Number 10 failed to condemn Andrew Sabisky’s appalling comments, but also seems to have endorsed the idea that white people are more intelligent than black people.

“Boris Johnson should have the backbone to make a statement in his own words on why he has made this appointment, whether he stands by it, and his own views on the subject of eugenics.”

And Ms Sturgeon said: “These are really not acceptable headlines for any government to be generating – or allowing to be generated. They need to get a grip fast and demonstrate some basic but fundamental values in terms of our public debate.”

Acting Liberal Democrat leader Ed Davey said: “When you have a prime minister who has referred to people as ‘picaninnies’ with ‘watermelon smiles’, it is sadly no surprise that Boris Johnson has signed off on Dominic Cummings recruiting someone with such extreme and offensive views.

“This Conservative government is a national embarrassment. By giving Dominic Cummings such power and then failing to control him, Boris Johnson is revealing who really is in charge.