The health secretary’s startling revelation came as he confirmed that London will be placed into the toughest tier 3 Covid restrictions from midnight on Wednesday.
More than 1,000 cases have been identified, mainly in the south-east of England.
But cases have also been found in 60 different local authority areas and “numbers are increasing rapidly”, Hancock said.
He told the Commons: “Over the last few days, thanks to our world class genomic capability in the UK, we have identified a new variant of coronavirus which may be associated with the faster spread in the south-east of England.
“Initial analysis suggests that this variant is growing faster than the existing variants.”
He went on: “I must stress at this point that there is currently nothing to suggest that this variant is more likely to cause serious disease.
“And the latest clinical advice is that it is highly unlikely that this mutation would fail to respond to the vaccine.
“But it shows we’ve got to be vigilant and follow the rules and everyone needs to take personal responsibility not to spread this virus.”
Hancock said the UK has notified the World Health Organisation about the new variant and Public Health England is continuing to analyse it at its Porton Down lab.
Commons health committee chair Jeremy Hunt asked Hancock when we would know for sure whether existing Covid vaccines work against the new variant.
Hancock said the strain was being assessed now but added: “The medical advice that we have is that it is highly unlikely that this new variant will impinge the vaccine and the impact of the vaccine.
“But we will know that in the coming days and weeks as the new strand is cultured at Porton Down, and then of course the tests conducted upon it.”
Scotland’s first minister Nicola Sturgeon said the new variant of coronavirus was “clearly a potentially concerning development” and was considering "whether any additional precautions are required".