Hundreds of early career researchers have warned the UK will lose a generation of scientists after the announcement of significant cuts to physics projects and research facilities.

Scientists working in particle physics, astronomy and nuclear physics have been told their grants will be cut by nearly a third, with project leaders asked to report back on how their research would fare with cuts up to 60%.

At the same time, the UK has shelved plans for four large infrastructure projects to save more than £250m. The projects include an upgrade to a detector on the Large Hadron Collider at Cern near Geneva, and an electron-ion collider under development with researchers in the US.

While the cost overruns are driven by facilities, the cuts are landing on physics grants as the science funding body UK Research and Innovation (UKRI) seeks to “do fewer things better” and prioritise applied research over more fundamental science.

In an open letter to Prof Ian Chapman, the chief executive of UKRI, more than 500 researchers write: “The present combination of uncertainty, delay and re-prioritisation in early career pathways risks the loss of a generation from the UK research and industrial ecosystem.”

Dr Simon Williams, a 29-year-old postdoc at Durham University, studies quantum computing applications in theoretical physics and is looking for a second postdoc position. “The only options I’ve realistically had are overseas,” he said. “As things stand, it is increasingly likely that I will take up a position in Germany rather than remain in the UK. There are simply far more viable and stable opportunities abroad.”

Dr Claire Rigouzzo, a 26-year-old researcher at King’s College London, has accepted a post in Europe after finding nothing in the UK. Early career scientists faced one of the harshest job markets in years, she said, but the knock-on effects were broader. Senior academics were worried because they cannot attract the best researchers, she said. “Even students can sense that science is no longer a priority,” she added. “Morale is extremely low across the board.”

UKRI has nearly £9bn to distribute through research councils this year, covering physical sciences and engineering, biological sciences and medical research. The Science and Technology Facilities Council (STFC) funds physics research as well as major facilities such as the Diamond Light Source in Oxfordshire.

The STFC needs to make £162m in savings by 2030 after seeing electricity costs spiral at its national facilities and subscriptions to international projects such as Cern and the European Space Agency rise with foreign exchange rates. The funder also committed to projects it can no longer afford.

Another King’s researcher, Dr Lucien Heurtier, 37, will come to the end of his contract in September and has started looking for jobs in China. “It is clear that no UK university will want to open lecturer positions in curiosity-driven research if such lecturers would not be able to attract much national funding,” he said. “My wife and daughter will have to follow.”

The loss of grants means the UK faces a situation where it has spent hefty sums on overseas projects such as the groundbreaking Rubin Observatory in Chile, which will swing into action this year, but could have no UK astronomers to work on it. “The timing of these proposed cuts, just as the telescopes start to deliver, could not be worse,” said Prof Catherine Heymans, Scotland’s astronomer royal.

Prof Mike Lockwood, the president of the Royal Astronomical Society, urged the government to step in to prevent a “catastrophe” in science. “You lose a whole generation,” he said. “The facilities side is overcommitted and it’s young researchers that are taking the brunt of that. As a nation, we can’t afford for that to happen.”

Speaking to reporters, Chapman defended the moves. “When you make choices there will be some things that miss out, but when you don’t make choices, everybody misses out because you choke everybody and nothing then can be internationally competitive because it’s all underfunded,” he said.