Daily Covid-19 cases have risen above 50,000 in the UK for the first time since July, as the prime minister resists calls for the government to activate its backup plan.

Official figures on Thursday put the number of positive tests at 50,009 as cases have continued to rise. The last time cases were at this level was 17 July. Daily data also showed 115 people died within 28 days of a positive test.

Boris Johnson told broadcasters during an interview in Northern Ireland on Thursday that he would not be switching to “plan B”.

The PM said: “We are continuing with the plan we set out in July. We are watching the numbers very carefully every day.

“The numbers of infections are high but we are within the parameters of what the predictions were, what Spi-M [modelling group] and the others said we would be at this stage given the steps we are taking. We are sticking with our plan.”

The Office for National Statistics, which has been doing research involving testing in the community, said that the number of people infected with the virus is at its highest point since January, just after a lockdown had been introduced.

On Wednesday the British Medical Association accused the government of being “wilfully negligent” for not reintroducing rules including mandatory face masks. The health secretary, Sajid Javid, used a press conference to encourage the public to use face coverings in crowded places but said further restrictions would not be introduced “at this point”.

On Thursday, the Labour leader, Sir Keir Starmer, said the government’s current plans were failing, but said he did not want ministers to change course for “plan B”.

He urged the government to commit to a target of 500,000 jabs a day. “The government said that the vaccine would be the security wall against the virus. And now the government is letting that wall crumble,” he said.

“The booster programme has slowed down so much that at this rate, we’re not going to complete it until spring of next year. The government needs to change, it needs to get a grip.”