"I can see nothing in the data at the moment that means we can't go ahead with step four of the opening on 21 June," he said.
"But we've got to be so cautious because there's no question the ONS (Office for National Statistics) data of infection rates is showing an increase.
"We always knew that was going to happen. Don't forget we always said the unlocking steps that we've taken would lead to increases in infection.
"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.
"There, I'm afraid, the data is just still ambiguous and so every day we're having long sessions where we're interrogating all the data, we're looking at all the various models.
"And the best the scientists can say at the moment, in their guidance to us, is that we just need to give it a little bit longer."