The NHS could soon be unable to deliver “the care it needs to” for women giving birth if the surge in Covid cases continues, the president of the Royal College of Obstetricians and Gynaecologists has said.

Dr Edward Morris, the UK’s most senior gynaecologist, became the latest high-ranking clinician to raise the alarm about the increasing pressures on the health service as Covid cases rise and it battles a huge backlog of 5.7 million patients caused by the first and second waves of the virus.

He told the Guardian he was increasingly concerned about the “immense pressures” facing maternity staff. The latest figures suggest the sharp rise in new cases reported in recent weeks is now having an impact on hospital numbers, with average daily Covid hospital admissions in England at their highest level for nearly eight months.

The latest data shows 39,962 people reported testing positive for Covid on Sunday with 328,287 testing positive in the last 7 days and 949 deaths during the same period.

Rishi Sunak on Sunday publicly ruled out “immediately” moving to the government’s coronavirus plan B, a suite of “light-touch” measures such as working from home and compulsory face masks in some settings. The chancellor said the data did not suggest such a move was necessary, despite reports that the UK Health Security Agency (UKHSA) was canvassing the level of support among local authorities for the “immediate rollout of the winter plan” – the clearest sign yet that Whitehall is actively considering additional measures.

Morris said the surge in Covid infections also threatened to derail efforts to tackle a huge backlog in cases of women waiting for gynaecological treatment. Senior doctors say operations are already being cancelled in some parts of the country.

Morris raised fears patient safety could be put at risk in maternity wards if the increase in Covid cases and hospitalisations resulted in specialist staff being redeployed to other parts of hospitals, as happened in the first coronavirus wave. “The Covid-19 pandemic is far from over and we’re becoming increasingly concerned about the immense pressures facing our maternity staff this winter if the situation continues as it is,” he said.

“We’re also aware of the many women and girls who are suffering with gynaecological conditions that are currently on extensive waiting lists with no end in sight. With the number of Covid-19 cases rising once more, the NHS could soon be in a situation where it is unable to deliver the care it needs to or deal with the huge backlog that has already built up.”

Morris added: “We know during the first wave of the pandemic, maternity staff were redeployed to different areas of the hospital, and we would urge NHS trusts and boards to avoid this at all costs.” Maternity staff could not be replaced by other staff groups “due to their specialist skill set”, he said, and protecting this workforce was “crucial to ensure that safe maternity care can be sustained”.

Morris urged unvaccinated pregnant women to urgently get jabbed. Figures show almost a fifth of the most critically ill coronavirus patients in England in recent months were unvaccinated pregnant women.

“We’re seeing higher numbers of pregnant women in critical care than at any other point during the pandemic and the vast majority of these women are sadly unvaccinated. Vaccination against Covid-19 and flu is the best way for pregnant women to protect themselves and their baby this winter.”

Both Labour and the Liberal Democrats have called for some plan B measures to be introduced and the NHS Confederation on Wednesday became the first major organisation to warn that rising cases risked derailing efforts to tackle the backlog.

Dr Katherine Henderson, the president of the Royal College of Emergency Medicine, warned on Sunday that emergency departments were in a “terrible place”.

She told Sky News’s Trevor Phillips on Sunday: “We’re already struggling to cope. This is not something that’s coming in the next couple of months. We’re already in a terrible place where we have got large queues of ambulances with vulnerable people waiting in those ambulances to be offloaded into departments and other patients at home waiting to be picked up by the ambulance.

“That’s the thing that really worries me; that these are patients who have not yet received treatment that we don’t necessarily know what’s wrong with them that we’re really struggling to get into our healthcare facilities to then work out what we need to do.”

Boris Johnson has previously said vaccines will get the country through the winter and out of the pandemic. But on Sunday Prof Adam Finn, who is on the Joint Committee on Vaccination and Immunisation (JCVI), said the vaccine programme would not be enough to bring infection rates under control. He said people should be testing themselves, wearing masks and avoiding crowds in enclosed spaces in order to prevent “a real meltdown” in what he described as a worsening situation.

While vaccines were very effective at stopping people from getting seriously ill, he said, they were not so effective at stopping infections altogether or stopping the virus spreading.

“They do have an effect on that, but they’re not by themselves going to be enough at the present time to keep the spread of the virus under control,” he told Phillips. “I would like to re-emphasise the fact that the vaccine programme by itself, in the current situation, even if things go optimally, is not, in my opinion, enough to bring things under control.”