Health secretary Matt Hancock told Sky's Sophy Ridge on Sunday that scenes of people leaving London in their droves were 'totally irresponsible'.
These photos and videos showed people leaving London and boarding a train to Leeds on Saturday evening, despite passengers on board realising that the train had been oversold and they were forced to abandon social distancing.
Mr Hancock said: "Especially in Tier 4 areas, everybody has to behave as if they might well have the virus.
"This is a deadly disease, we've got to keep it under control and it's just been made more difficult by this new variant."
He went on to talk about the rollout of the vaccine and the need to stick to new restrictions which have been put in place, adding: "We know with this new variant you can catch it more easily from a small amount of the virus being present.
“All of the different measures we have in place, we need more of them to control the spread of the new variant than we did to control the spread of the old variant. That is the fundamental problem.
“We know that because we know that in November that in the areas where this new variant started, in Kent, the cases carried on rising whereas in the rest of the country the November lockdown worked very effectively.
“It is an enormous challenge, until we can get the vaccine rolled out to protect people. This is what we face over the next couple of months.”
The new strain has been found in Yorkshire, but only 5% of cases are currently attributable to the new variant, Mr Hancock said.
Dr Chaand Nagpaul, BMA council chair, said that scenes of people packing onto trains to get out of London before new restrictions came into force would not be seen in east Asian countries which have managed to control previous pandemics.
When asked what action the Government could take he said that it was making sure there were crowd-control measures.
Dr Nagpaul added: “You would not see those scenes in east Asian countries that have managed pandemics well in the past.
“It’s more than rules, what I think is really important for the public to understand is this is an unforgiving virus.
“Whilst Christmas is obviously going to be ruined for many, the worst thing we could be doing is infecting our loved ones.
“That’s not being alarmist, that’s unfortunately the way this virus behaves.”
Dr Susan Hopkins, of PHE, said that the evidence that the new variant was up to 70% more transmissible was based on modelling the rate of increase in the new strain compared to others in circulation.
She told the Andrew Marr Show on the BBC that there was also evidence of people with the new variant having higher viral loads of the virus.
“We have seen evidence of the virus showing higher viral loads so there’s more virus in the people we are detecting with this virus strain,” she said.
But she said a higher viral load did not mean people were going to get more ill, adding: “The illness comes from the immune response and how it reacts in your lungs – that’s where we know the illness really starts to be driven from and why people need oxygen.
“The higher amount of the virus means that people are likely to be more infectious than they would otherwise be and this means we need to reiterate the social distancing measures.”