Leading scientists have warned that ongoing shortages of COVID tests across the UK are a “great concern” ahead of New Year’s Eve celebrations.

In recent days there have been widespread shortages of lateral flow and PCR tests for delivery on the government’s portal, with no PCRs available across the UK this morning.

Health Secretary Sajid Javid says the government will triple the supply of lateral flow tests to 300 million per month by February, but added that as current shortages persist “we expect to need to constrain the system at certain points over the next two weeks”.

Prof Ravi Gupta, clinical microbiologist at the University of Cambridge, told Sky News the lack of available tests is “a great concern because of course we already have so many cases that therefore the probability of an individual being in a social environment on NYE and being positive, even if they have potentially tested negative in the last 24 hours, is fairly high.”

He added: “The transmissions are going to be significant and of course the availability of tests… of lateral flow testing… is going to compound that problem. So I’m personally very worried about what’s going to happen next year.”

His advice to people planning to celebrate on New Year’s Eve was to try to test before attending an event, make sure others around them are testing, wear good quality masks and “keep things as small as possible”.

His warning comes as Health Secretary Sajid Javid admitted there is “unprecedented demand for both PCR and Lateral Flow Device tests” which has “inevitably placed strain on the testing system”.

In a letter to MPs, he said: “In light of the huge demand for LFDs seen over the last three weeks, we expect to need to constrain the system at certain points over the next two weeks to manage supply over the course of each day, with new tranches of supply released regularly throughout each day.”

He went on to promise that capacity would be ramped up in the New Year, with the government buying millions more lateral flow tests, bringing in new products and accelerating deployment to the public.

“We are also doubling our total delivery capacity with Royal Mail to 900,000 test packs and PCR tests a day. We are tripling the supply of LFDs in January and February from our pre-Omicron plan of 100 million to 300 million per month,” he added.

His letter comes as another expert and member of NERVTAG, Professor Peter Openshaw, warned it is “very worrying” that a shortage of tests could lead to people mixing over New Year’s without knowing whether they are infectious.

Prof Openshaw said parties are “perfect” for spreading coronavirus and he told Radio 4’s Today programme: “We do know that crowding together in poorly ventilated spaces, particularly if you are shouting over loud music and so on, is absolutely perfect in terms of transmitting this very, very highly transmissible virus.”

Meanwhile, chairman of the Royal College of GPs, Professor Martin Marshall, said the Omicron variant is still “spreading like wildfire” and causing “massive problems” for doctors’ surgeries.

He told Times Radio that GPs are seeing increasing numbers of patients with COVID-19 and increased numbers of staff are having to self-isolate.