British Prime Minister Boris Johnson said on Wednesday he would be cautious in lifting restrictions as it is still unclear how protected the population would be against a new surge of Covid-19 cases should lockdown end as planned in June.
Johnson has previously warned that the swift spread of the B.1.617.2 variant of concern first identified in India could derail his plans to end England's Covid restrictions on 21 June.
On Wednesday he said there was nothing in the current data to suggest that date would have to be pushed back, but he could not commit to a 21 June reopening either.
"I can see nothing in the data at the moment that means we can't go ahead with step four, or the opening up on June 21st, but we've got to be so cautious," he told reporters.
"What we need to work out is to what extent the vaccination programme has protected enough of us, particularly the elderly and vulnerable against a new surge, and there I'm afraid the data is just still ambiguous."
Johnson said that a recent rise in cases after the latest easing of restrictions was expected, adding that he had been in long meetings each day looking at the data with science advisors.
The current guidance from scientists was they needed more time for data on the impact of the variant, now known as the Delta variant, to accrue, Johnson said.
The roadmap for reopening England from lockdown included 5 week intervals between steps so the impact of each step to ease restrictions could be assessed before the next step was taken.