Under his roadmap for easing COVID measures, the prime minister hopes "all legal limits on social contact can be removed" under the last of those four stages, to come on June 21 at the earliest.
Asked how confident he was of reaching that target, Johnson said on Tuesday, "I'm hopeful but obviously nothing can be guaranteed and it all depends on the way we continue to be prudent and continue to follow the guidance in each stage, Sky News reported.
"That's why it's so important to proceed in the cautious way that we are.
"I think people do understand it, they can see the logic of what we're trying to do.
"But, genuinely, because of the immense possibilities now of the vaccination rollout, because science has given us this way of creating a whole shield around our population, we can really look at that June 21 date with some optimism.
"I'm very optimistic we'll be able to get there."