There is no data to suggest England's end to lockdown on 21 June might be delayed, the business secretary has said - but he cannot give a guarantee.

"I don't think we will move the date," said Kwasi Kwarteng - but added that the scientific evidence could change.

Some scientists believe the reopening date should be delayed until more people are fully vaccinated.

Most people in hospital in Bolton - a Covid hotspot - have only had one dose, a leading doctor there said.

"We have a significant numbers of 30 and 40-year-olds going in [to hospital] and obviously they've only really just in recent times become eligible," said Dr Helen Wall, who works on leading Bolton's vaccine programme.

The variant first identified in India is now believed to be responsible for up to three-quarters of new Covid cases in the UK.

Cases of the Indian variant are still mainly focused in hotspots such as Bolton, Bedford and Blackburn with Darwen - but most parts of the country now have small numbers of cases, Public Health England said.

Some health experts - such as Prof Christina Pagel, from University College London - believe the 21 June date - when all remaining restrictions in England are due to be lifted - should be delayed until a greater proportion of the population have had two doses.

Currently, 45.6% of the UK's adult population have had their second dose - around 24 million people - and this proportion is rising by roughly 5% every week.

"If we can just delay international travel, delay stage four of the roadmap until we have a much higher proportion of people vaccinated with two doses, we're in a much, much better position," said Prof Pagel.

"We're only two months away from that, it's not long to wait."

Prof Andrew Hayward, a member of the Sage advisory group, added: "I think there is a good argument for caution until such time as we've got a much higher proportion of the population double vaccinated."

Cases continue to rise across the UK - something that was always expected as lockdown eased - but the government has said the crucial thing is to see how that affects the number of people in hospital. That is among the most important data that will affect whether the 21 June date can go ahead.

"Nothing I've seen would suggest that we should extend or delay the date of reopening," Mr Kwarteng told BBC Radio 4's Today programme on Friday. "But the caveat obviously is the data can change.

"So if scientific evidence, data, points to an increased hospitalisation rate, an increased degree of risk, then we have flexibility to move that date. As of today, as of the data I've seen, I don't think we will move the date. But I can't guarantee that."

A final decision about the 21 June date will be reached by 14 June.

Scientists believe the Indian variant spreads more easily - and vaccines still work, although one dose is less effective than it was against the Kent variant.

Prof Hayward said people who have had two doses of the vaccine did not need to be "overly worried".

But he said: "On the other hand, if you've only had one dose of vaccine, then the protective effect appears to be about 30%."

The rules have recently changed so over-50s and people considered clinically vulnerable are being offered a vaccine eight weeks after their first - rather than 12 weeks.

On Thursday, the number of new Covid cases topped 3,000 for a second day in a row - 3,542 - the first-time infections have reached this level since early to mid-April. A further 10 people died with coronavirus, the government figures show.

Step four of the government's roadmap for lifting lockdown on 21 June would see all legal limits on social contact removed, nightclubs reopened, and restrictions on large events and performances lifted.

Boris Johnson was asked about the 21 June date on Thursday.

The prime minister said England "may need to wait" for the lifting of all restrictions but that there was nothing currently in the data to suggest there would have to be a delay.