Boris Johnson’s senior aide Dominic Cummings has been dragged further into the row over No 10’s decision to hire an adviser with eugenicist views after it emerged that he suggested in his own writings that the NHS should cover the cost of selecting babies to have higher IQs.

In a blogpost covering his views on the future of “designer babies”, Cummings said he believed rich would-be parents would inevitably select embryos with “the highest prediction for IQ” and floated the idea that “a national health system should fund everybody to do this” to avoid an unfair advantage for the wealthy.

Experts criticised Cummings’s theories about genetics, saying they were unworkable, unethical and amounted to eugenics, two days after Andrew Sabisky resigned as a No 10 contractor over his past claims that black Americans on average had lower IQs than white people.

Cummings’ drive to bring “misfits and weirdos” into Johnson’s team was central to the appointment of Sabisky, who it later emerged had also proposed enforced contraception to prevent the creation of an “underclass”.

Cummings’s writings do not make any reference to race in relation to genetics and intelligence, unlike Sabisky’s comments. But Labour and leading geneticists criticised Cummings for veering into the territory of eugenics – the practice of selection of desirable traits for the improvement of humans.

Conservative MPs and even some ministers who already fear that Cummings’ repeated involvement in controversies is damaging the government, were aghast when Sabisky’s comments came to light this week.

Cummings’ suggestion that the state could provide embryo selection by potential IQ to anyone who wants it will alarm critics who fear radical change to the NHS under Boris Johnson’s stewardship.

In a blogpost published in 2014 after he had attended a Silicon Valley science conference at Google’s HQ, Cummings proposed allowing people to select eggs for their babies that appeared to have the best chance of having a high IQ, if genes for high intelligence could be identified in the future.

He said this could allow rich people to become more intelligent than poorer people who could not afford expensive genetic screening, and said one way to combat the problem would be making embryo selection for intelligence available on national health services.

Such a practice would need a major change in the law in the UK as there are strict ethical guidelines on genetic screening for “designer babies” set out by the Human Fertilisation and Embryology Authority.

In the post, Cummings wrote: “It is already the case that farmers use genomes to make predictions about cows’ properties and behaviour … It is already the case that rich people could use in vitro fertilisation to select the egg which they think will be most advantageous, because they can sequence genomes of multiple eggs and examine each one to look for problems then pick the one they prefer. Once we identify a substantial number of IQ genes, there is no obvious reason why rich people will not select the egg that has the highest prediction for IQ.

“This clearly raises many big questions. If the poor cannot do the same, then the rich could quickly embed advantages and society could become not only more unequal but also based on biological classes. One response is that if this sort of thing does become possible, then a national health system should fund everybody to do this. (I.e. it would not mandate such a process but it would give everybody a choice of whether to make use of it.) Once the knowledge exists, it is hard to see what will stop some people making use of it and offering services to – at least – the super-rich.”

In a different blog discussing the practicality of screening embryos for medical defects, he acknowledged the difficulty of making arguments that touch on genes and their relation to intelligence but suggested society would move towards “more realistic” views on the issue.

“It ought to go without saying that turning this idea into a political/government success requires focus on A) the NHS, health, science, NOT getting sidetracked into B) arguments about things like IQ and social mobility. Over time, the educated classes will continue to be dragged to more realistic views on (B) but this will be a complex process entangled with many hysterical episodes. (A) requires ruthless focus,” he said.

His suggestions drew on the work of his friend Prof Stephen Hsu, a US physicist who has been working on a Chinese project to find genes for intelligence. Hsu and Cummings were pictured together outside Downing Street last year.

David Curtis, an honorary professor in the UCL Genetics Institute at University College London, said Cummings had “fundamentally misunderstood key concepts in genetics and his suggestions are wildly unrealistic”.

He said: “He seems to have got his ideas from a physicist rather than the genetics researchers who have a more thorough understanding of these topics. Cummings is proposing a form of eugenics which we actually know would never be effective. Measurable genetic variants have only a tiny influence on IQ and the testing he is proposing would be worse than useless.”

The professor, who is editor-in-chief of the Annals of Human Genetics, whose original title was the Annals of Eugenics, called the idea “ludicrous” and said: “It’s incredible to think that his proposals would involve creating 10 healthy fertilised embryos and then discarding nine of them, purely to select the one which scored highest on some completely illusory measure.”

Prof Richard Ashcroft, a medical ethicist at City University, called Cummings’ ideas “cargo cult science”. He added: “This idea that we can use biological selection to improve individuals and society, and that the state through the NHS, should facilitate this, really is pure eugenics.”

Bobbie Farsides, a professor of clinical and biomedical ethics at Brighton and Sussex Medical School, said the ideas floated in Cummings’ blog were far from the scientific mainstream. “In this country we’ve taken the decision to only use embryo selection as a way of combating serious disease,” he said. “We’ve not moved to thinking of it in terms of enhancement, be that intelligence or anything else. It would be such a huge step away from the fundamental values that inform embryo selection at the moment that it’s almost inconceivable. We are so many million miles away from this being on the agenda.”

Cummings’s ideas were also criticised by Andrew Gwynne, the shadow communities secretary, who said: “However Cummings tries to dance around his beliefs, it is clear that this is eugenics. Eugenics is a long-discredited and dangerous pseudo-science and should have no place in the 21st century, let alone be held by No 10.”

No 10 declined to comment on whether Cummings still held the same views on selection of genes for intelligence as expressed in the 2014 post. It has repeatedly refused to answer questions this week over whether Johnson agrees with Sabisky that black people have lower IQs on average.