Boris Johnson has been forced to delay the end of England's coronavirus restrictions by up to four weeks after being warned the move could lead to thousands of deaths and unbearable pressure on the NHS.

The British Prime Minister announced the setback to the final phase of his plan to end the lockdown next Monday due to concerns over the rapidly-spreading Delta variant first identified in India.

Experts feared going ahead with Step 4 on 21 June as planned could lead to hospital admissions on the scale of the first wave of Covid-19 heaping unsustainable pressure on the health service.

Mr Johnson told a Downing Street press conference that to avert this, the end of all legal limits on social contact would be put back to 19 July.

He hopes deaths will be significantly reduced by that point because two-thirds of adults will have then been offered both vaccine doses due to the delay being coupled with a reduction in the time between jabs for the over-40s.

Limits on numbers for sports events, pubs and cinemas will therefore remain in place, nightclubs will stay shuttered and people will be asked to continue working from home where possible.

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Downing Street left open the option of ending restrictions on 5 July if the data proves drastically better than expected but conceded this is "unlikely".

Mr Johnson did, however, announce a limited easing of restrictions to take place from 21 June as he faces the prospect of a rebellion from Conservative MPs who are furious about the delay.

The 30-person cap for wedding ceremonies and receptions, as well as wakes, will be lifted, with limits to be set by venues based on social distancing requirements.

Care home residents will also no longer need to self-isolate for 14 days after leaving for visits in most cases.

Fans were expected to be able to attend the Euro 2020 semi-finals and final in Wembley as the pilots on attendance of large events continue.

Mr Johnson felt he had to delay the relaxation after at least one of his four tests to easing restrictions - that the risks are not fundamentally changed by new variants - had been failed.

Officials also called into question the test to ensure infection rates do not lead to a surge in hospital admissions that could put unsustainable pressure on the NHS.

Modelling by the British government's Spi-M group suggested there was a possibility of hospital admissions reaching the heights of the first peak in March 2020 if the relaxation went ahead on Monday.

Experts believe the Delta variant is driving a rapid accelerations in cases, estimating it is between 40% and 80% more transmissible than the Alpha variant first found in Kent.

Ministers were expected to hold a vote in Parliament on Wednesday in order for the government to be given the legal powers to extend the restrictions.

Mr Johnson will hope the limited restrictions he has approved will reduce the scale of the rebellion on the Tory backbenches.

He told the press conference that there is a "real possibility the virus will outrun the vaccines".

He said for this reason, the decision had been made to "give the NHS a few more crucial weeks to get those [Covid vaccine] jabs into the arms of those who need them".

How effective are vaccines against the variants?

A previous study by Public Health England (PHE) found that the Pfizer coronavirus vaccine is 88% effective against the variant first identified in India (the Delta variant) after two doses.

This compares with 93% efficacy against the variant first identified in Kent (the Alpha variant).

Meanwhile, the AstraZeneca jab was 60% effective, compared with 66% against the Alpha variant over the same period.

Both vaccines were 33% effective against symptomatic disease from the Delta variant three weeks after the first dose, compared with about 50% against the Alpha variant.

A separate PHE study found that Covid-19 vaccines are "highly effective" in preventing hospital admission with the Delta variant of coronavirus.

PHE's study of hospital admissions found that the Pfizer/BioNTech vaccine is 94% effective against hospital admission after just one dose, rising to 96% after two doses.

And the Oxford/AstraZeneca vaccine is 71% effective against hospital admission after just one dose, rising to 92% after two doses.

Unvaccinated people have twice the risk of hospital admission with the Delta variant as the Alpha variant.

Protection against death is also expected to be high, but further work is underway to confirm this, PHE said.