During a visit to a vaccination clinic in Milton Keynes on Wednesday, Mr Johnson urged people to get tested before attending New Year’s Eve festivities.

“Everybody should enjoy New Year, but in a cautious and sensible way – take a test, ventilation, think about others but, above all, get a booster,” he said.

On Wednesday Sir Roger Gale, the veteran Tory MP, said Mr Javid had called him after he expressed concerns about the lack of availability of tests in Kent and had told him the problem would take time to sort out.

Sir Roger, the MP for North Thanet, said: “Saj was very honest with me. He said: ‘Look, there isn’t a quick fix.’

“We are now facing the situation where Number 10 is saying ‘go and get tested’ and the Department of Health is saying ‘we haven’t got the tests, we can’t do it’. We have created demand in England which we now can’t satisfy.”

Sir Roger said Mr Javid was “busting a gut” to get supplies “but we’re competing with a global market”.

The Government put out a call to suppliers for an additional 500,000 PCR tests a day two weeks ago, setting Dec 27 as a deadline for applications, one source said.

A Department of Health source said: “Yes, there is a lot of demand that will put pressure on the system – but we have got a lot of supply. We are doing everything we can to make sure people can get the tests they want. If people are not able to get it the first time, if they try again in a couple of hours they should be OK.”

Lord Lansley, who was health secretary from 2012 to 2014, urged ministers to be ready to slash self-isolation times from seven days to five days next week when more data was ready.

He told The Telegraph that “if the risks of omicron are less, then the costs of responding to it should be less too. They could argue responsibly to leave it a fortnight, but they should prepare to go to five days next week”. But he said he was concerned about a shortage of tests needed to allow people to be released early from self-isolation.

Chloe Smith, the work and pensions minister, said it was “sensible to monitor” whether cases increased from cutting self-isolation from seven to five days, but said there were “no current plans” to move to a five-day model.