Sir Keir Starmer has urged resident doctors not to go ahead with “reckless” strikes planned for next week, saying it is “beyond belief” they could take place during a flu outbreak.

The prime minister said the NHS is in its “most precarious moment” since the coronavirus pandemic due to soaring flu cases across the UK, and that strikes would put the healthcare system and its patients in “grave danger”.

The doctors’ union, the British Medical Association (BMA), is polling its members to see if they are willing to call off the walkout, with the results to be released on Monday.

But if they vote against it, a five-day strike by resident doctors will begin two days later on Wednesday 17 December.

A BMA spokesperson said the government could stop the strike by tackling pay, conditions and trust with a credible offer.

Flu has come early this winter, and it looks to be a particularly nasty season because of a new mutated version of the virus which is circulating, say experts.

Many are now calling it “super flu”, but it is not more severe nor harder to treat.

An average of 2,660 patients per day were in hospital with flu in England last week – the highest for this time of year since records began in 2021, and up 55% on the week before, NHS England said.

Flu cases are also rising in Scotland, Wales and Northern Ireland, figures show.

Children and young people are particularly affected by the outbreak, health officials said.

Writing in the Guardian, Sir Keir said the strikes “should not happen” and said resident doctors, formerly known as junior doctors, should accept a deal to avert industrial action.

Sir Keir said as well as the government’s new offer, they had also given the BMA the chance to reschedule the strikes until after Christmas.

“Don’t get me wrong – of course I would rather they were cancelled… But under the circumstances, I wanted to be sure we have left no stone unturned in our efforts to protect the NHS,” he said.

The BMA said it will ask its members whether the government’s offer will be enough to call off Wednesday’s strikes.

If members indicate yes, then they will be given time to consider the offer in more detail and a formal follow-up referendum would be held on ending the dispute completely.

The offer aims to address problems for some doctors trying to find work and to provide more training places for newly qualified medics to progress in their careers.

Health Secretary Wes Streeting made a similar intervention to Sir Keir’s on Friday, warning strikes coupled with increasing flu patients would be a “double whammy” for the NHS.

However, the medical director for the NHS in London, Chris Streather, said the flu situation was “well within the boundaries” of what the NHS could cope with and that hospitals were better prepared for large disease outbreaks since the Covid pandemic.