Britain was preparing Sunday to move to the next phase of its coronavirus vaccination programme, as it neared a target of inoculating 15 million of the most vulnerable people.

The country will start administering vaccines from Monday to those aged between 65 and 69 and the clinically vulnerable to Covid-19, with almost 1.2 million already invited to book their jabs, the state-run National Health Service (NHS) said.

The step comes after the government was set to meet its aim to have offered vaccinations to the top four priority groups of around 15 million people by the end of this week.

That comprises all over-70s, care home residents and staff, NHS workers and the extremely clinically vulnerable to the virus.

The government said Saturday more than 14.5 million had received a first dose.

And Foreign Secretary Dominic Raab said it was "on track" to meet the "important milestone" and officials could now focus on vaccinating all over-50s by May and all adults by September.

"(It is) the first milestone towards the wider plan to get 99 percent of those at risk of dying (from Covid-19) vaccinated with a first dose by the end of April, and then everyone in the country... by the autumn," he told Sky News.

Britain, which has been the hardest hit in Europe by the pandemic, registering nearly 117,000 deaths within 28 days of a positive Covid-19 test, began its biggest ever vaccination campaign in early December.

It now has one of the highest proportions of people vaccinated against the virus in the world.

'Cautious' easing

Meanwhile, infection rates have dropped markedly across the country over recent weeks, as strict lockdown measures have curbed previously spiralling case numbers, hospitalisations and deaths.

The improving situation has prompted calls for stringent lockdown restrictions to be lifted in early March, despite concern about the spread of virus variants that may be more resistant to vaccines.

A new 10-day hotel quarantine regime for British residents returning from 33 virus variant hotspots begins on Monday, despite criticism that the move is too little and too late.

Prime Minister Boris Johnson said Saturday he is "optimistic" he will be able to set out plans for a "cautious" easing of the stay-at-home rules in England later this month.

He has vowed to review all relevant data next week, ahead of setting out the government's "roadmap" for the months ahead on February 22.

But he is facing pressure from some of the government's own lawmakers.

Lockdown-sceptic Conservatives have called on Johnson to commit to a timetable for completely ending the controls by May.

In a letter to the British premier, the leaders of the Covid Recovery Group of Tory MPs, said the "tremendous pace" of the vaccination rollout allowed for the move.

"The vaccine gives us immunity from Covid, but it must also give us permanent immunity from Covid-related lockdowns and restrictions," they wrote.

"All restrictions remaining after March 8 should be proportionate to the ever-increasing number of people we have protected."