Pressure is mounting on the Government to rethink the easing of Covid-19 restrictions over Christmas with leading medical journals warning the move could “cost many lives”.

The British Medical Journal and Health Service Journal have written a joint editorial for only the second time in 100 years to call on the Government to rethink their strategy.

They said that the Government “is about to blunder into another major error that will cost many lives”.

The warning, authored by HSJ editor Alastair McLellan and BMJ editor-in-chief Fiona Godlee said: “When Government devised the current plans to allow household mixing over Christmas it had assumed the Covid-19 demand on the NHS would be decreasing.

“But it is not, it is rising, and the emergence of a new strain of the virus has introduced further potential jeopardy.

“Members of the public can and should mitigate the impact of the third wave by being as careful as possible over the next few months. But many will see the lifting of restrictions over Christmas as permission to drop their guard.

“The Government was too slow to introduce restrictions in the spring and again in the autumn.

“It should now reverse its rash decision to allow household mixing and instead extend the tiers over the five-day Christmas period in order to bring numbers down in the advance of a likely third wave.”

Member of the Government’s Scientific Advisory Group for Emergencies (Sage) Sir Mark Walport said people need to be “extraordinarily careful” in the run-up to Christmas.

Speaking in a personal capacity, the former chief scientific adviser told BBC Radio 4’s Today programme: “The sad fact is that when people gather and mix, particularly in indoor environments, that is conducive to the virus moving around. And it’s as simple as that.

“People should think. If they are going to be mixing in households which have older people in them, then they really do need to be extraordinarily careful in the week or so before Christmas comes.”

Asked what would happen if people are not careful enough, Sir Mark said: “I think the consequences are obvious – an increase in numbers and the need for a more prolonged social distancing, and Tier 3 measures in parts of the country after Christmas.”

Professor Calum Semple said people would have ignored any ban on Christmas gatherings.

But the Sage member told BBC Breakfast: “If you do go round and camp in Granny and Grandpa’s house for five days, that’s going to be dreadful.

“If they go round for the Christmas meal, then perhaps the family should be doing the cooking and the washing up and treating Granny and Grandpa like the king and queen.

“But if they do do lots of hugs and kisses, then the virus will spread.

“So this is about meeting your friends and family, ideally doing the best you can to wash your hands, maintain some social distancing, meeting outside when you can, and trying to stay safe.

“But clearly lockdowns work because lockdowns reduce social interaction and that reduces the virus.

“If you stop your lockdown, stop your tiers, have huge amounts of social interaction, there will be a rise in cases.”

The relaxation of rules over Christmas looms as Health Secretary Matt Hancock revealed over 1,000 people in the UK have tested positive for a “new variant” of coronavirus.

Speaking to the Commons, Mr Hancock said: “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 of England.”

Matt Hancock said the numbers of the new variant of coronavirus “are increasing rapidly”.

He told the Commons: “Initial analysis suggests that this variant is growing faster than the existing variants.

“We’ve currently identified over 1,000 cases with this variant predominantly in the South of England although cases have been identified in nearly 60 different local authority areas.

“And numbers are increasing rapidly.”