All adults aged 50 and over should receive a coronavirus vaccine by May, the Government has announced.
Ministers had previously refused to give a firm date, saying only that the first nine priority groups would be vaccinated by the spring.
Downing Street repeatedly declined to define when spring ends during a briefing for journalists on Thursday.
But the Cabinet Office announced on Friday morning that the Government intended to vaccinate all nine groups by May.
It said the UK's vaccination programme planned to have reached all nine priority cohorts by May - which it said gave the Government confidence to commit to holding local elections that month.
Categories five to nine include all those aged 50 and over, as well as adults aged 16-65 in an at-risk group.
According to the Government's vaccines delivery plan, some 27 million people in England - and 32 million people across the UK - are estimated to fall in the first nine groups.
The Government is on track to vaccinate the first four cohorts by February 15 - including NHS and care home staff, care home residents, and all those aged 70 and over.
So far, more than 10.4 million people in the UK have received their first dose of a coronavirus vaccine.
Prioritisation for the rest of the population has yet to be determined.
But there are reports that the UK is considering introducing a vaccine passport, so Brits can go on holiday abroad if they've been vaccinated.
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Foreign Office minister James Cleverly said it would be up to the individual countries where holidaymakers are arriving to decide on their own border arrangements.
But he said it was "not an uncommon practice" for countries to require documents on inoculations and that the Government would work with international partners on this.
It follows reports in the Times that British officials have started work on an official certification programme after Greece said it would waive quarantine rules for arrivals who can prove they have been vaccinated against Covid-19.
