The Prime Minister is expected to announce today that the end of lockdown will be delayed by four weeks.

The final legal social distancing restrictions were due to be lifted on June 21, which would have seen limits removed on gatherings and nightclubs reopen.

It was part of step four of Boris Johnson's lockdown roadmap, which was set as no earlier than June 21.

But it has been widely reported this morning that the PM will announce a four-week delay because of concerns over the Delta variant, first seen in India and now the dominant strain in the UK.

The variant is thought to be up to 60 per cent more transmissible than the so-called Kent variant, which had been the dominant strain through the winter.

It will see the new 'freedom day' signposted for July 19.

Mr Johnson is set to hold a press conference at 6pm tonight where he is expected to announce the measures.

He is expected to appeal to the public to show patience, with one last push to ensure that when controls do finally end it is “irreversible”.

However, it comes as a huge setback to many businesses – particularly in the battered hospitality sector – which had pinned their hopes on a full summer reopening to recoup some of the losses of the past year.

There was deep frustration among lockdown sceptics on the Conservative benches who said there was no reason not to end the restrictions as those most at risk of death or serious illness are now fully vaccinated.

Former minister Mark Harper, the chairman of the Covid Recovery Group (CRG) of Tory MPs, said any postponement would be a “political choice”.

He warned that if the unlocking did not go ahead as planned, restrictions could carry on through the autumn and into the winter as other respiratory infections picked up.

“The effectiveness of our vaccines at preventing hospitalisation means unlocking on June 21 could proceed safely. Any decision to delay will be a political choice,” he said.

“Variants and mutations will appear for the rest of time. We have to learn to live with it.

“If our very effective vaccines cannot deliver us freedom from restrictions, then nothing ever will.”

Mr Johnson, Chancellor Rishi Sunak, Health Secretary Matt Hancock and Cabinet Office minister Michael Gove were reported to have been briefed by the chief medical officer Professor Chris Whitty and the chief scientific adviser Sir Patrick Vallance.

The latest daily Government figures from Sunday showed another rise in infections with a further 7,490 lab-confirmed cases in the UK – up 2,149 from a figure of 5,341 the previous week.

The data also had England with a total of 35,971 positive tests in the past seven days at a rate of 63.9 per 100,000 people.

Foreign Secretary Dominic Raab indicated at the weekend that they wanted to use the additional time to get millions more younger people double-jabbed.

He said that while the vaccines had weakened the link between infections and hospital admissions, they wanted to be sure it was “severed and broken”.

The cautious approach was, he said, necessary to ensure the the unlocking was “irreversible” and that they did not have to “yo-yo back in and out of measures”.

When setting out the four stages of the roadmap out of lockdown earlier this year, the PM had included four tests that would need to be met on each occasion.

They are: the vaccine deployment programme continues successfully; evidence shows vaccines are sufficiently effective in reducing hospitalisations and deaths in those vaccinated; infection rates do not risk a surge in hospitalisations which would put unsustainable pressure on the NHS; and assessment of the risks is not fundamentally changed by new Variants of Concern.