Prime Minister Boris Johnson on Wednesday raised the prospect of the UK proceeding with its planned roadmap to end lockdown restrictions from June 21 as he said that there is nothing in data to suggest that a delay would be necessary.

Speaking at 10 Downing Street, he struck a note of caution as there are clear signs the there is a rise in infection rates from the so-called Delta variant of COVID-19 a highly transmissible mutation first identified in India and behind what some scientists fear may be the early signs of a third wave of the pandemic in the UK.

"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," said Johnson.

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, he said.

His comments came as the National Health Service (NHS) released latest vaccination figures, which show that half of all adults in England are now fully vaccinated against COVID-19 and three-quarters have received a first dose.

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, said Johnson.

"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," he added.

In recent days, the UK Prime Minister has faced growing calls from different sections of experts and scientists to delay a complete end to lockdown restrictions due to the continuing spread of the Delta variant.

On Tuesday, the UK recorded zero deaths from COVID-19 for the first time since last year and triggered calls from members of Johnson's own Conservative Party to not derail the lockdown roadmap.

June 21 will mark the fourth and final stage of the government's roadmap for easing coronavirus rules dubbed "freedom day" as all legal limits on social contact are scheduled to be lifted.

Johnson acknowledged the wait for a clear answer would be "frustrating" for people ahead of stage four of his roadmap, a deadline hospitality venues have been eagerly looking forward to.

On Wednesday, the UK recorded a further 4,330 infections and another 12 coronavirus deaths.

Sir John Bell, professor of medicine at University of Oxford and part of the government's vaccine taskforce, told the BBC that the UK's "numbers don't look too intimidating" and he was "encouraged" by what he saw. However, he said the government was taking "a wise approach" in being cautious ahead of making its decision.

"I do think we need to keep our eye on hospitalisations, serious disease and deaths which is really what we are trying to manage," he said.

"If we scamper down a rabbit hole every time we see a new variant we are going to spend a long time huddled away so we do need to keep a bit of balance to the discussion and keep our eyes on the serious disease that we are trying to prevent," he added.

A final decision on whether restrictions will be relaxed will be reached on June 14.