Boris Johnson has not ruled out a third national lockdown amid rising rates of coronavirus, as health chiefs warn of the toll on frontline staff and services from festive mixing.

The Prime Minister said rates of infection have increased “very much in the last few weeks”, as pressure grows on the Government to do more to tackle the rise.

Northern Ireland and Wales are bracing for lockdowns in the days after Christmas, and a senior emergency medicine doctor said the rest of the UK must do “whatever it takes” to get infections under control.

Speaking during a visit to Bolton, Greater Manchester, Mr Johnson was asked whether England would follow Northern Ireland in imposing stringent restrictions after the festive period.

He said: “We’re hoping very much that we will be able to avoid anything like that. But the reality is that the rates of infection have increased very much in the last few weeks.”

Schools minister Nick Gibb earlier insisted England’s tier system, which will see swathes of southern and eastern England move to the toughest restrictions from Saturday, is “very effective”.

But he added “we rule nothing out” when asked about the possibility of a national lockdown after Christmas.

Labour leader Sir Keir Starmer called on Mr Johnson to set out his plan for averting a third lockdown, something he said would be “hugely damaging on health grounds” as well as for the economy.

The Opposition leader suggested limiting Christmas to mixing only between two households instead of three would be a “step in the right direction” and that numbers within households could also be considered.

The president of the Royal College of Emergency Medicine, Dr Katherine Henderson, described a “real perfect storm” for hospitals as they try to balance increased numbers of Covid-19 patients with non-Covid work and a lack of beds.

She told the PA news agency: “It seems to me we need to do whatever it takes to get the situation firmly under control so that we can vaccinate people and then move forward.”

In other developments:

– The latest figures from the Scientific Advisory Group for Emergencies (Sage) show the reproduction number, or R value, of coronavirus transmission across the UK is estimated to have risen to between 1.1 and 1.2.

– PA analysis of Public Health England data showed London, eastern England and south-east England have Covid-19 case rates that are higher than when the second lockdown began in England on November 5.

– Advice from a coalition of education unions said secondary schools and colleges that are unable to set up mass testing of students for the first week of January should not be forced to.

– President Donald Trump said a second coronavirus vaccine, made by Moderna, has been approved for use in the US. The jab, of which the UK Government has secured seven million doses, is still under consideration for approval here by the Medicines and Healthcare products Regulatory Agency (MHRA).

– US Vice-President Mike Pence received his first jab of the Pfizer vaccine live on television.

Mr Johnson has reiterated his warnings to people to see the five-day Christmas relaxation period as “very much a maximum – that’s not a target people should aim for”.

He added: “Keep it short, keep it small, have yourselves a very little Christmas as I said the other night – that is, I’m afraid, the way through this year.

“Next year I have no doubt that as we roll out the vaccine and all the other things that we’re doing, it will be very, very different indeed.”

In Scotland, the option for a post-Christmas lockdown “remains on the table”, Health Secretary Jeane Freeman said.

Northern Ireland will see a six-week lockdown introduced from December 26 to curb rising cases – with the closure of non-essential retail and contact services, as well as restricting the hospitality sector to takeaway only.

Wales will go into its third full lockdown from December 28 amid a “sustained rise in coronavirus”.

Dame Donna Kinnair, chief executive and general secretary of the Royal College of Nursing, said nurses would not enjoy Christmas “knowing what awaits them in January”, amid fears of what she predicted could be an “unrelenting tsunami” of cases following relaxed restrictions.

She said ministers should give “fresh and more detailed” advice to the public with a week to go until Christmas.

Professor Neil Ferguson, whose modelling led to the original lockdown in March, suggested a third national lockdown may need to be more stringent than the one England emerged from at the beginning of December.

He told BBC Radio 4’s World At One programme: “The concern I have right now is that… (in) the East of England, for instance, case numbers were rising during the last lockdown, so there may be a need for additional controls beyond even what were in place then.”

Dr Nick Scriven, immediate past president of the Society for Acute Medicine, said a period of mixing next week “strikes fear into the hearts of clinicians on the front line”.

New figures from the Office for National Statistics suggest half of adults across the country are planning to form a Christmas bubble.

The survey, carried out between December 10 and 13, before Mr Johnson urged people to scale back their festive plans, also found that fewer people are planning social activities such as meeting in pubs, cafes or bars, compared with last year.

Up to three households are able to mix in England, Northern Ireland and Scotland between December 23 and 27, but the limit is two households in Wales.

Travel to and from Northern Ireland is also permitted on December 22 and 28.

The ONS said the proportion of people in private households testing positive for Covid-19 is estimated to have increased sharply in London, with other increases in Eastern England, the East Midlands and south-east England, while rates have continued to decrease in north-west England and Yorkshire and the Humber.