Boris Johnson has refused to rule out imposing a third national lockdown on England in the new year, saying the reality is infections rates are rising.

Northern Ireland will enter a tough six week lockdown beginning on Boxing Day in an attempt to suppress a surge in Covid-19 cases.

Asked on Friday if England could soon follow, the prime minister 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.”

It comes as the Office for National Statistics (ONS) said the proportion of people testing positive is estimated to have increased sharply in London.

Infection rates have also increased in Eastern England, the East Midlands and south-east England, the ONS said.

The East Midlands has the highest rate (with an estimated 1.4% of people in private households testing positive for Covid-19), followed by London (1.4%) and north-east England (1.2%). South-west England has the lowest rate (0.4%).

Much of England is currently under strict tier 2 or tier 3 restrictions, but the rules will be loosened from December 23 until December 27.

Under the relaxed rules, three households will be allowed to mix over the five day period.

But Johnson urged the public to now think of that as a “maximum” not “a target people should aim for”.

“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,” he said.

“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.”

ONS figures published on Friday showed half of adults across the country are planning to form a Christmas bubble.

But the survey was carried out before the Johnson urged people to have a “smaller, safer Christmas” due to Covid fears.