The easing of Covid-19 lockdown rules due to take place on June 21 have been delayed by four weeks, Boris Johnson has confirmed.
The final step of the PM’s roadmap - which was to remove most remaining restrictions in England - is now expected to take place from July 19.
But in a blunder set to spark confusion - the Prime Minister wrongly said during televised Covid-19 briefing that the unlocking would be delayed until "July 29."
Some relaxation will go ahead from June 21, with rules eased for weddings, wakes and care homes.
And more people will be able to get a Covid-19 vaccine earlier, under new plans being brought forward today.
But most remaining rules, including limitations on mixing indoors, mask wearing in shops and on public transport, and guidance to work from home where possible, will stay in place.
The Government put the brakes on after two of the four tests used to measure the risk of easing the rules were not met - as the Delta variant continued to rip through the country.
Experts fear this would lead to “surge in hospitalisations which would put unsustainable pressure on the NHS”.
The Prime Minister’s official spokesman said there has been a “rapid acceleration in cases” - and experts believe England could suffer a wave of hospitalisations as bad as the first wave last April if step four went ahead on June 21.
Nationally there are around 8,000 new cases per day, the highest since February.
Ministers have been told cases are growing at 70% week-on-week and in around a third of the country, are doubling every week.
Hospitalisations are increasing by 15% week-on-week and by 66% in the North West.
More than 3,000 new UK patients per day were being admitted at the height of the first wave - compared to under 200 a day now.
The PM’s official spokesman confirmed: “SPI-M modelling suggests if we were to go ahead with step four on Monday, there is a possibility of hospitalisations around the peak of the first wave.”
The PM’s official spokesman said the extension means “thousands more deaths can be prevented” as it gives time to get more people jabbed.
There will be a two-week review of the delay on June 28, and the PM’s official spokesman said if data is “much better than expected”, restrictions could then be eased on Monday 5 July.
But the spokesman added this outcome is “unlikely”.
There is no guarantee step four will not be delayed again, and the move to step four will only be confirmed on July 12.
But Boris Johnson’s official spokesman said: “The Prime Minister is confident we will not need any more than a four-week delay”.
To take advantage of the pause, the government has officially brought forward its July 31 target to offer a first vaccine dose to all adults in England.
Instead it now aims to offer all over-18s a first dose of the vaccine by July 19 - the new date step four should take effect.
At the same time, ministers have set a new target to offer all eligible over-40s in England a second dose by July 19 at the latest.
To achieve this, all over-40s will now be offered their second dose eight weeks after their first - not 12 weeks, as is the case now.
The dose “interval” had already been shortened for over-50s, but that will now happen for people in their 40s as well.
No10 said people in their 40s will be contacted to change their appointment date for their second dose, so they do not need to contact the NHS or their GP themselves.
These changes should mean two-thirds of adults have been offered both doses by July 19.
The 30-person limit on weddings will be removed in England from June 21.
That means there will be no numerical limit on either receptions or ceremonies - either indoors or outdoors - with the only restrictions being based on social distancing and venue capacity.
This is the approach that is already taken to funerals - and will now also apply to wakes.
MPs will be given a vote on extending the current regulations beyond their current expiry date, June 30. A debate and vote in both the Commons and the Lords will start on Wednesday.
Labour has already indicated it would vote for a delay to unlocking - meaning the vote is likely to pass.
Health Secretary Matt Hancock will address the Commons on the measures at 8.30pm - something which has provoked anger from Speaker Lindsay Hoyle.
Sir Lindsay accused Downing Street of "running roughshod" over MPs by not informing them first of any changes.
Speaking in the Commons on Monday afternoon, Sir Lindsay said: "Can I just say, we weren't going to get a statement until I got involved with Downing Street.
"The fact is this has been forced to actually get a statement today, it was going to be left to tomorrow, which would have been totally unacceptable.
"The fact is - I understand the Prime Minister at the moment is on Nato, there is a big conference going on, he isn't here - that's why I insisted that somebody came to make this statement. The timing of it is 8.30pm. I thought that was better than waiting for the Prime Minister to make a statement tomorrow.
"This House needs to know, it needs to know first. I find it totally unacceptable that once again, once again, that we see Downing Street running roughshod over members of Parliament. We're not accepting it and I'm at the stage where I'm beginning to look for other avenues if they're not going to treat this House seriously.
"But I will say I think it's time for me to have a meeting with the Prime Minister to actually put on the record here now but with him that this House matters."
He was responding to points of order from two senior Conservative MPs, Peter Bone and Sir Edward Leigh, who both voiced their unhappiness with the handling of the announcement.
Mr Bone, Conservative MP for Wellingborough, said to MPs: "It's a long-standing principle of this House that major changes to Government policy are announced to Parliament first.
"I can think of no more important policy announcement than changes to regulations that restrict the freedom of the British people."
He went on: "What makes this matter more concerning is that about 30 minutes ago the media were given an Embargoed copy of the statement.
"So the media have the statement in advance, there will be a public press conference at 6pm and the last people to know about the changes to the Covid regulations will be members of Parliament.
"This is clearly very disrespectful to Parliament and probably a contempt of Parliament."