Boris Johnson is to abolish any immigration restrictions on top scientists to counter fears that the UK’s research reputation could be seriously damaged by a no-deal Brexit.

The prime minister will instruct the Home Office and the Department for Business, Energy and Industrial Strategy to work on a new plan to ease entry to the UK for scientists ranging from those based at prestigious institutions to promising students who have won maths Olympiads.

Downing Street sources suggested Johnson believed the UK should have sent signals immediately after the referendum that it would ease visa restrictions on skilled migrants to counter claims that the leave vote was anti-immigration, a policy rejected by Theresa May.

Q&A What does a no-deal or WTO-rules Brexit mean? Show Hide If the UK leaves the EU without a deal it would by default, become a “third country”, with no overarching post-Brexit plan in place and no transition period. The UK would no longer be paying into the EU budget, nor would it hand over the £39bn divorce payment. The UK would drop out of countless arrangements, pacts and treaties, covering everything from tariffs to the movement of people, foodstuffs, other goods and data, to numerous specific deals on things such as aviation, and policing and security. Without an overall withdrawal agreement each element would need to be agreed. In the immediate aftermath, without a deal the UK would trade with the EU on the default terms of the World Trade Organization (WTO), including tariffs on agricultural goods. The UK government has already indicated that it will set low or no tariffs on goods coming into the country. This would lower the price of imports – making it harder for British manufacturers to compete with foreign goods. If the UK sets the tariffs to zero on goods coming in from the EU, under WTO “most favoured nation” rules it must also offer the same zero tariffs to other countries.

WTO rules only cover goods – they do not apply to financial services, a significant part of the UK’s economy. Trading under WTO rules will also require border checks, which could cause delays at ports, and a severe challenge to the peace process in Ireland without alternative arrangements in place to avoid a hard border.

Some no-deal supporters have claimed that the UK can use article XXIV of the General Agreement on Tariffs and Trade (Gatt) to force the EU to accept a period of up to 10 years where there are no tariffs while a free trade agreement is negotiated. However, the UK cannot invoke article XXIV unilaterally – the EU would have to agree to it. In previous cases where the article has been used, the two sides had a deal in place, and it has never been used to replicate something of the scale and complexity of the EU and the UK’s trading relationship. The director general of the WTO, Roberto Azevêdo, has told Prospect magazine that “in simple factual terms in this scenario, you could expect to see the application of tariffs between the UK and EU where currently there are none”. Until some agreements are in place, a no-deal scenario will place extra overheads on UK businesses – eg the current government advice is that all drivers, including lorries and commercial vehicles, will require extra documentation to be able to drive in Europeif there is no deal. Those arguing for a “managed” no deal envisage that a range of smaller, sector-by-sector, bilateral agreements could be quickly put into place as mutual self-interest between the UK and EU to avoid introducing or to rapidly remove this kind of bureaucracy. Martin Belam

Though the proposed new criteria remain relatively vague, Johnson said he wanted the immigration system to be changed to make the UK a far more attractive place for scientists to be based.

“We were home to the world’s first national DNA database, we discovered graphene, and our cutting-edge scientists should be proud to follow in the footsteps of titans like Ada Lovelace and Nobel laureates Francis Crick and Peter Higgs,” he said.

“But to ensure we continue to lead the way in the advancement of knowledge, we have to not only support the talent that we already have here, but also ensure our immigration system attracts the very best minds from around the world.”

Measures could include abolishing the cap on numbers under the tier 1 exceptional talent visas, even though the scientific community recently raised concerns about a low uptake from scientists of these types of specialised visas, rather than demand being too high.

Other parts of the package could include expanding the pool of UK research institutes and universities able to endorse candidates, ensuring scientists’ dependants can join them and work and that they have an accelerated path to settlement.

But the proposals were ridiculed by the discoverer of graphene, the Nobel prize-winning physicist Prof Sir Andre Geim. He told the Times: “The government may try and reduce the barriers to entry for scientists but they cannot reduce turmoil that would be caused to science in the UK by a no-deal Brexit. Scientists are not fools. They know that turmoil is inevitable for many years.”

Geim said his fellow Nobel laureate, Prof Sir Konstantin Novoselov, had left their base in Manchester, where the pair discovered graphene, after the 2016 vote to leave the EU. “I think that tells you everything you need to know,” he added.

Johnson announced the plans on a visit to the Culham Centre for Fusion Energy near Abingdon, Oxfordshire, which is a national research laboratory.

Johnson said the government would provide additional funding for scientists and researchers who sought EU funding before the UK’s withdrawal from the EU, and any Horizon 2020 applications stuck in the approval process when the UK left would be reviewed automatically and successful applications provided with funding.

The UK already has a system for fast-tracking some much-needed foreign science professionals into UK roles. A number of science professions are included on the official shortage occupation list, which allows firms to employ non-EEA migrants without having to advertise the role.

Among the roles are biological scientists and biochemists, physical scientists, and social and humanities scientists, including archaeologists.

Though there have been instances of high-profile scientists leaving the UK because of visa issues, the problems have almost always been with restrictions on family members. Ensuring visas for dependants is among the measures that No 10 has suggested it could offer to attract scientists to the UK.

Quick guide What Vote Leave leaders really said about no-deal Brexit Show Hide Boris Johnson, prime minister Johnson told the Treasury select committee in March 2016: “Our relationship with the EU is already very well developed. It doesn’t seem to me to be very hard … to do a free trade deal very rapidly indeed.” Speaking at a Vote Leave event in March 2016, Johnson said: “I put it to you, all those who say that there would be barriers to trade with Europe if we were to do a Brexit, do you seriously believe that they would put up tariffs against UK produce of any kind, when they know how much they want to sell us their cake, their champagne, their cheese from France? It is totally and utterly absurd.” Johnson, then foreign secretary, told the House of Commons in July 2017:“There is no plan for no deal because we are going to get a great deal.” Dominic Raab, foreign secretary Two months before the June 2016 referendum vote, Raab told Andrew Neil on BBC Sunday Politics: “We’re very well placed, and mutual self-interest suggests we’d cut a very good deal and it’s certainly not in the European’s interests to erect trade barriers.” During an appearance on the BBC’s Daily Politics in April 2016, Raab added: “The idea that Britain would be apocalyptically off the cliff edge if we left the EU is silly.” Michael Gove, chancellor of the duchy of Lancaster In April 2016, Michael Gove said the UK would have the best of both worlds. “Outside the EU, we would still benefit from the free trade zone which stretches from Iceland to the Russian border,” he said. “But we wouldn’t have all the EU regulations which cost our economy £600m every week.” Liam Fox, former international trade secretary After the referendum, in July 2017, the then-international trade secretary Liam Fox said: “The free trade agreement that we will have to do with the European Union should be one of the easiest in human history. We are already beginning with zero tariffs, and we are already beginning at the point of maximal regulatory equivalence, as it is called. In other words, our rules and our laws are exactly the same.” Simon Murphy and Frances Perraudin

Last year Fengying Liu, a postdoctoral researcher in pathology, was recruited to Oxford’s Sir William Dunn School of Pathology in October but left her post after the Home Office refused a visa for her 22-month-old child.

The House of Commons science and technology committee heard evidence from the Royal Society last year that uptake of tier 1 visas was low, meaning the cap was never being reached.

Prof Richard Catlow told the committee of MPs: “The big issue with tier 1 is that we need to get a higher proportion of uptake … With the other academies, we have been addressing the factors that led to a lower than desirable uptake for one scheme.”

Norman Lamb, the Lib Dem MP who chairs the science and technology committee, said the changes would need to go beyond easing restrictions on the most prestigious scientists.

“Often people will bring a team with them, of lab technicians and researchers, so you need smooth access for them,” he said.

Lamb said the preoccupation for the industry was the effects of no deal on access to funding and collaboration.

The committee has recommended the government ease visa restrictions on scientists, researchers and skilled workers post-Brexit, including those only eligible for the lower tier 2 visa.

Leading scientists have recently warned about the effect of no-deal Brexit on research collaboration and the UK’s status as a leading research hub.

The chair of the Wellcome Trust, Eliza Manningham-Buller, told the BBC last month that the vast bulk of the collaborations were with Europe and any new restrictions could lead to UK scientists being cut out of projects.

In a letter sent to the prime minister in July, Lady Manningham-Buller said: “Wellcome spends around £1bn a year to support research, and most of our money is spent in the UK because it has a thriving sector. Leaving the EU without a deal is a threat to that. I am afraid that some damage has already been done, with loss of researchers, and influence.”