Every day of Christmas freedom will result in two extra days of tighter restrictions, health chiefs have warned.

Dr Susan Hopkins,  chief medical adviser to NHS Test and Trace, told a Downing Street briefing that Sage scientific advice indicated that "for every day that we release (measures) we will need two days of tighter restrictions".

"So, coming into Christmas we need to be very careful about the number of contacts that we have, to reduce transmission before Christmas and get our cases as low as possible."

As the Prime Minister faces mounting pressure to allow families to be together over the festive period, Dr Hopkins said: "Hopefully the Government will make the decision that will allow us to have some mixing, but we will wait and see what that is.

"Then, I think, once we have got past the Christmas period if there has been a release and some socialisation we will all have to be very responsible and reduce those contacts again."

The R rate has been dropping, the latest data shows

Credit: Number 10 Downing Street

Dr Hopkins said that ministers are working on what the "new tiers" will be after the anticipated easing date for lockdown and on a plan for Christmas.

Asked about how Christmas may look like, she told the Government data briefing: "This is a decision that will be made by Government and I know that they’re working hard to develop an outline of what that will look like and what the new tiers will look like post-December 2 and what Christmas will look like."

Households across the country are set to be banned from mixing when lockdown ends under Government plans to rescue Christmas, The Telegraph understands.

Boris Johnson has repeatedly promised that the national lockdown will be replaced with a "regional tiered approach" when it ends on December 2.

But Government sources say default restrictions across the country are likely to include a ban on mixing with other households until close to Christmas.

Ministers intend to announce an "end of lockdown package" next week, including a schedule for Britain’s vaccination programme and an expansion of mass testing, which they hope will soften the blow of further restrictions.

The plans aim to allow a loosening of restrictions for Christmas, with scientists suggesting a number of households might be allowed to "bubble" together for a short period. Christmas bubbles could last for five days.

The number of people testing positive for coronavirus in England is still growing, but less quickly in recent weeks

Credit: Number 10 Downing Street

Deputy chief scientific adviser Dame Angela McLean said it would not be a problem easing England’s lockdown if the R rate remained above one next week, due to the lag in calculating the value.

Speaking at the same briefing, she said: "The way we estimate R is very dominated by lagging indicators – people who are in hospital or people who have died.

"People who are going in to hospital now are people who got infected weeks ago."

She said that an increase in people’s activity on the day before England’s lockdown came into effect was a "worry to us".

"You can imagine why people would want to get some shopping in before the shops were all shut," she said.

Asked whether that was a concern when considering measures ahead of Christmas, she said: "We are concerned about how can we have a safe run-up to Christmas so that we can some kind of a good family Christmas."

Dame Angela indicated the Sage advisory panel had been examining potential relaxation of measures over Christmas, saying: "We did send some advice in over the weekend.

"But we genuinely don’t know what decisions have been made."

Asked whether households mixing could be allowed if there were other trade-offs, Dame Angela said: "What’s really important is we go into a festive week when we want to mix with our friends and our family with the number of infections in the community as low as possible."