Health chiefs have urged anyone who travelled to regions from Tier 4 areas or Wales to self-isolate, turn away Christmas Day visitors and “assume” they have the new Covid-19 variant.

On Monday afternoon, public health directors in the West Midlands and Greater Manchester asked people to self-isolate for 10 days if they had travelled from London and areas of the South East, which entered Tier 4 at the weekend, or Wales, where tough new measures came into force on Sunday.

In Liverpool City Region, where a mass coronavirus testing pilot has been taking place, anyone who had travelled from London or the South East to the area was urged to get a coronavirus test.

Director of public health for the Lancashire authority of Blackburn with Darwen Dominic Harrison told BBC Lancashire anyone who had travelled from a Tier 4 area since last Wednesday should self-isolate for at least five days.

The advice came after scenes of people packing railway stations in London hours before Tier 4 controls came into force at midnight on Sunday, prompting fears the more infectious new variant could be spread across the country by the travellers.

Director of public health for Tameside, Greater Manchester, Dr Jeanelle de Gruchy said: “The new strain of Covid, which is increasingly rapidly in Tier 4 areas, is extremely worrying.

“It is incredibly infectious and if you come in to contact with someone with this strain you are far more likely to catch it than the original strain.

“We are so concerned about the potential grave impact of this that we have taken the difficult decision to ask anyone who has travelled here for Christmas from any Tier 4 area or Wales to act as if they have this new variant, even if they have no symptoms, and self-isolate for at least 10 days.

“Other people in the house do not need to self isolate but no visitors should be allowed in that house at all, even on Christmas Day.”

A statement issued on behalf of all the West Midlands health chiefs also urged people to “self-isolate for at least 10 days”.

“This means remaining inside the house where they’re staying for the whole 10 days,” they said.

“Other people who live in the house do not need to self-isolate unless they get symptoms, but no visitors should be allowed in that house at all, even on Christmas Day.

“Even if you have a negative test, you should continue to self-isolate.”

The statement sent by the West Midlands Local Resilience Forum on behalf of the Strategic Co-ordinating Group added that, although the West Midlands is not in Tier 4, “it is highly likely that the new variant is circulating” in the region.

Asked about the advice at a Downing Street press conference, the Government’s chief scientific adviser Sir Patrick Vallance said local health directors “need to make decisions that they need to make” to ensure their local population is looked after.

“The new variant is spread around the country,” he said.

“It’s localised in some places but we know there are cases everywhere, so it’s not as though we can stop this getting into other places, there’s some there already.

“The message has been very clear and, I think I want to reinforce it, is stay local.

“I mean, people shouldn’t be travelling around the country at the moment.”

The impact of the new variant had an immediate effect at the weekend, with Prime Minister Boris Johnson also scrapping a planned five-day easing of restrictions, instead limiting the relaxation to just December 25.