The UK’s Covid-19 alert level has been lowered as the country’s top medics said the threat of the NHS being overwhelmed has receded.

The Level 5 alert was announced on January 4 as lockdown measures were introduced by Boris Johnson amid fears the health service could be swamped within 21 days.

The decision to reduce the alert to Level 4 has now been made by the UK’s four chief medical officers and NHS England’s medical director because the number of cases in hospital are “consistently declining”.

England’s Professor Chris Whitty, Northern Ireland’s Dr Michael McBride, Scotland’s Dr Gregor Smith, Wales’s Dr Frank Atherton and NHS England’s Professor Stephen Powis announced the decision on Thursday following advice from the Joint Biosecurity Centre.

They said health services across the four nations “remain under significant pressure with a high number of patients in hospital”, but thanks to the efforts of the public numbers are now “consistently declining, and the threat of the NHS and other health services being overwhelmed within 21 days has receded”.

They added: “We should be under no illusions – transmission rates, hospital pressures and deaths are still very high.

“In time, the vaccines will have a major impact and we encourage everyone to get vaccinated when they receive the offer.

“However for the time being it is really important that we all – vaccinated or not – remain vigilant and continue to follow the guidelines.”

Chris Hopson, chief executive of NHS Providers, said the alert level may have dropped but there was a “long way to go yet”.

He said that “no-one in NHS (is) anywhere near declaring this phase of battle won”.

The announcement came as Education Secretary Gavin Williamson defended his plans for the replacement of cancelled A-level and GCSE exams in England.

He insisted results decided by teachers will be fair amid concerns the plan will lead to grades being inflated.

Mr Williamson confirmed to MPs that “no algorithm” will be used to decide grades this summer, with the judgment of teachers relied on instead and any changes made by “human intervention”.

Exam boards will carry out checks to “root out malpractice”, he said.

Addressing the Commons about plans for grading, he said: “Ultimately, this summer’s assessments will ensure fair routes to the next stages of education or the start of their career. That is our overall aim.”

It comes as the Government prepares to publish details of who will be next on the priority list for a vaccine once all the over-50s and most vulnerable have been inoculated.

The Joint Committee on Vaccination and Immunisation is understood to have recommended that prioritisation should continue down the age ranges, with people in their 40s invited next for a jab.

The move could come as a blow to those who have been campaigning for teachers, police officers and other frontline key workers to be next on the list.

In other developments:

– Government data up to February 24 showed a further 448,962 first doses of vaccine and 31,613 second jabs had been administered.

– A further 323 people had died within 28 days of testing positive for Covid-19 as of Thursday and there had been a further 9,985 lab-confirmed cases in the UK.

– Surge testing was being carried out in Ealing, west London and Redbridge, east London after cases of the South African coronavirus variant were found.

Prime Minister Boris Johnson said the plans for teachers to grade pupils were a “good compromise” as he backed Mr Williamson following last year’s exams fiasco.

He said the process of issuing grades to students will be “fair” and “durable”.

In 2020 thousands of A-level students had their results downgraded from school estimates by a controversial algorithm before Ofqual announced a U-turn which allowed them to use teachers’ predictions.

Conservative MP Robert Halfon, who chairs the Commons Education Committee, asked how ministers will ensure there will not be a “wild west of grading” this summer.

Mr Williamson said grade inflation was an “important issue” but it was being addressed through internal and external checks.

The Education Policy Institute (EPI) think tank warned the latest plans could cause “extremely high” grade inflation.

Mr Williamson told MPs that exam boards would issue “grade descriptions” to help ensure teachers’ marks were consistent.

Schools will be given wide flexibility in deciding how teachers assess and grade pupils, based on the parts of the curriculum they have been taught.

Results will be published earlier than usual, with A-level grades issued on August 10 and GCSE students receiving their results two days later.

The move is expected to allow more time for pupils unhappy with their grades – particularly A-level students looking to secure university places – to submit appeals.

After the exams fiasco last summer, Mr Williamson resisted demands for his resignation, although the chief regulator at Ofqual and the most senior civil servant at the Department for Education both stepped down, leading to accusations that officials were being scapegoated.