Mr Sunak said: “We have worked with our EU partners to make sure that this is right deal for the UK, unlocking unparalleled research opportunities, and also the right deal for British taxpayers.”
Scientists called the announcement “tremendous news”.
Horizon is a collaboration involving Europe’s leading research institutes and technology companies which sees EU member states contribute funds that are then allocated to individuals or organisations on merit.
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The UK was negotiating a deal to remain in the €95.5bn programme, but talks stalled over Brexit-related disagreements such as Northern Ireland.
In the two years since the UK was removed, Downing Street has stepped in to match EU grant money lost.
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However, scientists warned that UK researchers have been missing out on collaboration with colleagues in Europe.
Professor Paul Stewart, from the Academy of Medical Sciences said the return “marks a pivotal moment for UK science”.
“After a hiatus, the scientific community is celebrating the tremendous news that we are once more part of the EU’s flagship funding programme,” he said.
“Health research is an international endeavour, it relies on supporting the best ideas, but also on creating cross-border networks which is good news for the UK, Europe and the rest of the world.
“Association sends a very strong message that the UK is open for business and remains a prime destination to work on health research and innovation to improve lives.”
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The government said UK researchers can apply for grants and bid to take part in projects under the Horizon programme from today.
As well as Horizon the UK will join the EU’s space programme, Copernicus, but it will not take part in the bloc’s nuclear technology scheme, Euratom.
Deal ‘not mission creep back into EU’
The breakthrough comes after months of talks between London and Brussels.
It had been hoped that a British return to Horizon would follow in the wake of the Windsor Framework deal, agreed in February and designed to address concerns over post-Brexit arrangements in Northern Ireland.
Whitehall sources said in July a draft deal was with the prime minister – but Downing Street said a UK-based alternative known as Pioneer also remained an option because Mr Sunak was concerned about “value for money”.
Michelle Donelan, the secretary of state for science, denied the move was “mission creep back into the EU”.
She told Sky News: “This is fantastic news, not just for British scientists and researchers but also the British taxpayer.
“What we’re announcing today is a great deal, a deal that many said we won’t be able to get.”
Under the terms of the deal, the UK will not need to pay into the scheme for the two years it was absent with costs under the programme beginning again in January 2024.
The government also pointed to the inclusion of a so-called “clawback” mechanism, which will mean that the UK will be compensated if British scientists receive significantly less money than the UK puts into the programme.
Ms Donelan said the deal also includes an overperformance indicator, which means the UK won’t be penalised for overperforming “so we can really back our British scientists to achieve”.
Newly-appointed shadow science secretary Peter Kyle told broadcasters that ministers now need to “get on with it”.
“What we’re missing out on is two years’ worth of innovation,” the Labour MP said.
“Two years of global companies looking around the world for where to base their research centres and choosing other countries than Britain, because we are not part of Horizon… This is two years of wasted opportunity for us as a country.”
Hiscox, the London-listed insurer, is close to naming a new chairman nearly eight months after the drowning of Jonathan Bloomer on the luxury yacht of technology tycoon Mike Lynch.
Sky News has learnt that Hiscox has narrowed its search to candidates including Richard Berliand, who chairs the interdealer broker TP ICAP.
Insurance insiders said that Mr Berliand was among fewer than a handful of potential successors to Mr Bloomer.
The sinking of the Bayesian off the Sicilian coast last August claimed the lives of Mr Lynch and his daughter, along with five other passengers, including Mr Bloomer.
A former boss of Prudential, Mr Bloomer was a well-liked figure in the City.
He had chaired Hiscox for just a year when he died.
The identities of the other candidates being considered by the company were unclear on Monday.
Asian stock markets have fallen dramatically amid escalating fears of a global trade war – as Donald Trump called his tariffs “medicine” and showed no sign of backing down.
Hong Kong’s Hang Seng index of shares closed down 13.2% – its biggest drop since 1997, while the Shanghai composite index lost 7.3% – the worst fall there since 2020.
Taiwan’s stock market was also hammered, losing nearly 10% on Monday, its biggest one-day drop on record.
Elsewhere, Japan’s Nikkei 225 lost 7.8%, while London’s FTSE 100 was down 4.85% by 9am.
US stock market futures signalled further losses were ahead when trading begins in America later.
At 4am EST, the S&P 500 futures was down 4.93%, the Dow Jones 4.32% and the Nasdaq 5.33%.
Markets are reacting to ongoing uncertainty over the impact of President Trump’s tariffs on goods imported to the US, which he announced last week.
Image: A screen showing the Hang Seng index in central Hong Kong. Pic: Reuters
Speaking on Air Force One on Sunday, Mr Trump said foreign governments would have to pay “a lot of money” to lift his tariffs.
“I don’t want anything to go down. But sometimes you have to take medicine to fix something,” he said.
The US president said world leaders were trying to convince him to lower further tariffs, which are due to take effect this week.
“I spoke to a lot of leaders, European, Asian, from all over the world,” Mr Trump told reporters.
“They’re dying to make a deal. And I said, we’re not going to have deficits with your country.
“We’re not going to do that because to me, a deficit is a loss. We’re going to have surpluses or, at worst, going to be breaking even.”
Mr Trump, who spent much of the weekend playing golf in Florida, posted on his Truth Social platform: “WE WILL WIN. HANG TOUGH, it won’t be easy.”
President Trump believes his policy will make the US richer, forcing companies to relocate more manufacturing to America and creating jobs.
However, his announcement has shocked stock markets, triggered retaliatory levies from China and sparked fears of a global trade war.
Reality hits that trade war no longer just a threat
China’s announcement of its tariff retaliation came late afternoon on Friday local time.
Most Asian markets closed shortly after – and markets in China, Hong Kong and Taiwan were closed for a public holiday – meaning the scale of the hit did not play out until today.
This morning we are getting a sense of the impact. Dramatic falls across all Asian markets clearly signal a realisation a global trade war is no longer just a threat, but a reality here to stay, and a global recession could yet follow.
Up until Friday, China’s response to Donald Trump’s tariffs had been perceived as restrained and designed to avoid escalation, the markets had reacted accordingly.
But that all changed last week when Mr Trump’s new 34% levy on all Chinese goods was matched by China with an identical tax. Both sit on top of previous tariffs levied, meaning many goods now face rates in excess of 50%.
These are numbers that make most trade between the world’s two biggest economies almost impossible and that will have a global impact.
China has clearly decided any forthcoming pain will have to be managed, and not being seen to be cowed and bullied by Mr Trump is being deemed more important.
But the scale of the retaliation will have further spooked the markets as it makes the prospect of negotiation and retreat increasingly unlikely.
Mr Trump added to the atmosphere of intransigence when he told the media on Sunday the trade deficit with China would need to be addressed before any deal could be done. The complete lack of concern from the White House over the weekend will also not have helped.
While smaller economies like Japan, South Korea, Cambodia and Vietnam are all lining up to attempt to negotiate, there are a lot of nations in that queue.
There is a sense none of this will be easily rectified.
US customs agents began collecting Mr Trump’s baseline 10% tariff on Saturday.
Higher “reciprocal” tariffs of between 11% and 50% – depending on the country – are due to kick in on Wednesday.
Investors and world leaders are unsure whether the US tariffs are here to stay or a negotiating tactic to win concessions from other countries.
Richard Flax, chief investment officer at wealth manager Moneyfarm, said: “I guess there was some hope over the weekend that maybe we would see this as part of the start of a negotiation.
“But the messages that we’ve so far seen suggest that the President Trump is comfortable with the market reaction and that he’s going to continue on this course.
Goldman Sachs has raised the odds of a US recession to 45%, joining other investment banks that have also revised their forecasts.
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In the UK, Sir Keir Starmer has promised “bold changes” and said he would relax rules around electric vehicles as British carmakers deal with a new 25% US tariff on vehicles.
The prime minister said “global trade is being transformed” by President Trump’s actions.
KPMG has warned tariffs on UK exports could see GDP growth fall to 0.8% in 2025 and 2026.
The accountancy firm said higher tariffs on specific categories, such as cars, aluminium and steel, would more than offset the exemption on pharmaceutical exports, leaving the effective tariff rate around 12%.
Yael Selfin, chief economist at KPMG UK, said: “Given the economic impact that tariffs would cause, there is a strong incentive to seek a negotiated settlement that diminishes the need for tariffs.
“The UK automotive manufacturing sector is particularly exposed given the complex supply chains of some producers.”
Traders called this morning a complete bloodbath as the UK’s FTSE 100 joined world indexes in turning red as uncertainty over Donald Trump’s tariffs continued to batter stock markets.
The cause is not just the imposition of those tariffs (the largest the US has inflicted since the 1930s) and the very obvious drag this will have on global trade and growth, but also the uncertainty of ‘what next?’.
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Investors cannot work out if the Trump administration is genuinely wedded to tariffs on this scale, on the proviso that they will help re-shore companies and millions of jobs to the United States.
They don’t know if they are permanent or merely part of a negotiating tactic to address trade imbalances, and for America to use its economic heft to strike better deals.
If Mr Trump is open to deals (the first test comes later in a meeting with the Israeli prime minister), markets will calm, even if the midst of uncertainty hasn’t fully cleared.
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17:21
Time to change tactics with Trump?
However, if this is a genuine rewiring of global trade and the end of globalisation as we know it, markets and economies will continue to get battered.
As one Trump supporter, billionaire Bill Ackman – who opposes the tariffs – put it, President Trump has launched a “global economic war against the whole world” that will usher in an “economic nuclear winter.”