The UK Health Secretary told MPs cases had doubled in the past week and were rising among all age groups.
Making a statement in the Commons, Mr Hancock urged the public to get the vaccine if they could, explaining that many of those infected were eligible, but had not yet got the jab.
He said: “There’s now 2,323 confirmed cases of B.1617.2 in the UK – 483 of these cases have been seen in Bolton and Blackburn with Darwen, where it’s now the dominant strain.
“Cases there have doubled in the last week and are rising in all age groups.
“In Blackburn, hospitalisations are stable with eight people currently in hospital with Covid, and in Bolton 19 people are now in hospital with coronavirus – the majority of whom are eligible for a vaccine, but haven’t yet had a vaccine.
“This shows the new variant is not tending to penetrate into older, vaccinated groups and it underlines again the importance of getting the jab especially – but not only – amongst the vulnerable age groups.
"The early evidence suggests that B1617.2 is more transmissible than the previously dominant B1117 variant.
"We do not yet know to what extent it is more transmissible.
“While we also don’t have the complete picture on the impact of the vaccine, the early laboratory data from Oxford University corroborates the evidence from Bolton Hospital and the initial observational data from India that vaccines are effective against this variant.”
Mr Hancock explained the UK Government has now “surged in” its rapid response team to Bolton and Blackburn, with 100 people visiting this past weekend.
He said: “We’ve installed six new testing units, we’ve brought in over 50 new vaccinators and set up two new vaccination centres, as well as extending opening hours and capacity at our existing sites.
“In Bolton, we’ve quadrupled the rate of vaccination. We carried out 6,200 vaccinations over this weekend.”
The senior Tory minister also reiterated the message that people taking the vaccine when offered it “will help us all get out of this pandemic”.
He continued: “It has been really heartening, I am sure the whole House will agree, to see the videos that have been published over the weekend of people queuing up to get the jab.
“To anyone who feels hesitant, not just in Bolton or Blackburn, but to anyone who feels hesitant about getting the vaccine right across the country, just look at what is happening in Bolton Hospital where the majority of people in hospital with coronavirus were eligible for the jab, but have chosen not yet to have the jab and have ended up in hospital – some of them in intensive care.
“Vaccines save lives, they protect you. They protect your loved ones and they will help us all get out of this pandemic.”
Mr Hancock also revealed people aged 37 would be offered the vaccine from Tuesday and this would be expanded further “later in the week”.
Labour’s shadow health secretary Jonathan Ashworth labelled the country’s borders as “secure as a sieve”.
He told the Commons: “The delay in adding India to the red list surely now stands as a catastrophic mis-step.
“One month ago in this House I urged him to act quickly in response to this variant.
"The Sanger Institute data today shows rapid increase in this variant – 30 per cent of all sequenced cases in the UK – and that excludes cases from travel and surge testing.
“Alarm bells should be ringing because while he offers reassurance that vaccines are effective, we’ve also heard from Professor Anthony Harnden of the JCVI recently who has warned that vaccines are ‘almost certainly less effective’ at reducing transmission of this variant.
“I entirely appreciate that he can’t offer a cast iron assurance about opening up on June 21. And I’m not going to try to push him into a corner. We are dealing with uncertainties.
"And we should be grown up about these things. But we need a plan to contain this variant urgently.”
It came as Scotland recorded 161 new Covid-19 cases in the past 24 hours, but no deaths.