A rise in the Indian variant of Covid in the UK could threaten the plan for England to come out of all restrictions next month.
Surge testing is taking place in 15 areas across England in a bid to identify and isolate cases.
"I have to level with you, this new variant could pose a serious disruption to our progress" Boris Johnson warned the nation at an unscheduled televised Covid briefing from Downing Street this morning (NZT).
Cases of the variant first found in India have more than doubled in the past week in parts of north-west England. The town of Bolton in Greater Manchester has seen a sharp spike in infections since mid-April.
In hopes of clamping down on the spread of the variant first found in India, Johnson announced the rollout of second doses for over 50s and the clinically vulnerable will accelerate across England, as he confirmed the planned lockdown easing will go ahead on Monday (local time).
"The good news is that so far we have no evidence to suggest that our vaccines will be less effective in protecting people against severe illness and hospitalisation."
"More investigation into where the new variant is much more transmissible is needed," he added.
His announcement comes as Glasgow and Moray in Scotland will now remain at Level 3 of the nation’s five-tier system for another week because of the new variant. The rules will ease for mainland Scotland from Monday (local time).
According to Our World in Data, almost 19 million people in the UK, around 28 per cent of the population, were fully vaccinated as of May 12. Almost 36 million people, about 54 per cent of the UK's population, had received one jab.