New 'mutations of concern' of the Covid-19 virus have been found in Liverpool and Bristol, Matt Hancock has confirmed.
The health secretary said that 11 new mutations have been identified in Bristol, with another 32 in Liverpool.
The government is also stepping up its door-to-door testing drive, which is currently underway in eight postcodes where the South African variant has spread.
"In all these areas it is imperative that people must stay at home and only leave home where it is absolutely essential," Hancock told the Commons on Tuesday
"When your local authority offers you a test you should take up the offer, because we know that one in three people with coronavirus have no symptoms but can still pass it on.
"We're offering testing to everyone aged 16 and over, even if you have been vaccinated.
"And if you live in one of those areas but have not been contacted and you're unsure if you should have a test, I encourage you to visit your local authority website to find out."
Hancock stated that there was no evidence that the South African mutation was any more dangerous, but it did appear to be more transmissible.
"We have to come down on it hard - our mission must be to stop its spread altogether," the health secretary added.
Door-to-door testing is set to take place in eight postcodes in England where the South African mutation has been discovered.
The eight areas are Hanwell, west London (W7), Tottenham, north London (N17), Mitcham, south London (CR4), Walsall in the West Midlands (WS2), Broxbourne in Hertfordshire (EN10), Maidstone, Kent, (ME15), Woking in Surrey (GU21) and Southport, Merseyside (PR9).
People in those areas are being urged to "think twice about their actions."
Universities minister Michelle Donelan told
BBC Breakfast that people should be having a "conversation with their employer about making sure that they can work from home" and "limiting even more the time that they are outside of their house".
