Downing Street has taken emergency action to head off winter pressures in the NHS amid growing fears in government that a healthcare crisis could derail the Tory party’s general election campaign.

The prime minister Boris Johnson has been holding regular meetings at No 10 with the head of NHS England, Simon Stevens, as evidence mounts of lengthening delays in treatment caused by shortages of doctors and nurses. In addition, the health secretary Matt Hancock has been seeing Stevens every week, on Monday mornings, to assess how to prevent a deterioration in waiting times at hospitals and GP surgeries.

The Observer has also learned that No 10, in an unprecedented move, has been planning to set up its own NHS “operations unit” as evidence mounts of lack of capacity and increasing waits for patients at A&E departments and on hospital trolleys.

On Saturday the British Medical Association issued a highly critical statement, saying it should not take a general election to prompt the government to act. It also warned that the NHS was now in a “perpetual state of crisis”.

NHS sources said No 10 wanted to have continuous knowledge of where pressure was building up in A&E departments, in cancer care and for routine operations such as hip replacements, cataract removals or hernia repairs. It is thought to be the first time any prime minister has sought to have such direct oversight of the service. “It’s really a form of micro-management,” said an NHS source.

Johnson and Hancock are also said to be considering giving the NHS another emergency cash boost to help it cope. If awarded, the money would be used to pay for increased social care support, to try to stop hospitals getting overcrowded, and also hire more agency staff to help keep services running. “There’s a debate going on about whether the government should give more money for that purpose to try and protect itself,” said a source.

The BMA council chair Dr Chaand Nagpaul said: “Under this government’s watch, patients and staff working in the NHS have endured winter after winter of overcrowded emergency departments, long delays and pitifully low staffing levels.

It should not take an election to take stock of just how bad the situation has become Dr Chaand Nagpaul, BMA

“It should not take an election to take stock of just how bad the situation has become. Staff are already coming under extreme pressure, trolley waits are at a worryingly high level, A&E targets are not being met and as such, the BMA predicts that the NHS is hurtling towards an unprecedented crisis this winter.”

Nagpaul added: “We need to see investment, both immediately to avert the coming winter crisis, and in the long term to address the perpetual state of crisis the NHS is now in.”

A mounting threat to capacity has been caused by the increasing reluctance of doctors to do extra shifts because they are being hit with huge unexpected tax bills of tens of thousands of pounds related to the rise in the value of their pensions, leading to operations being cancelled and “rota gaps” in hospitals.

Sarah Wollaston, who served as chair of the all-party select committee on health and social care in the last parliament, said the government had only itself to blame: “The pensions crisis issue is one the committee has been warning about for months, but the government has done nothing.”

The BMA is understood to have warned ministers in its submission for the cancelled November budget that the number of patients waiting on trolleys this winter is set to soar this winter.

The latest Opinium poll for the Observer today puts the Tories on 42%, 16 points ahead of Labour on 26%, with the Liberal Democrats on 16% and the Brexit party on 9%. But with more voters citing the NHS as the most important issue facing the country (59%) than Brexit (52%) the Conservatives, who will launch their manifesto on Wednesday, are aware a crisis could provide an opportunity for Labour to claw its way back.

The shadow health secretary Jonathan Ashworth wrote to Stevens on Saturday night demanding to have the same regular meetings and briefings as Hancock, saying he could be running the NHS after 12 December and needed to be aware of the extent of the crisis.

Ashworth said: “Expert after expert is warning that we’re heading into the worst winter on record for the NHS. We are set to see yet again shameful scenes of our elderly and vulnerable languishing on trolleys in corridors or trapped in ambulances because A&Es are so overcrowded. Estimates that trolley waits will climb as high as 300,000 – far in excess of last year – are staggering and reveal patients are set for a winter of Tory misery.”

The Department of Health and Social Care said: “Work to prepare for winter this year is already well under way. We have invested £240m in adult social care to ease pressures this winter by getting patients home quicker and freeing up hospital beds across England, on top of an extra £1bn capital funding this year to better equip our hospitals and maintain buildings in the face of rising demand.

“We have also backed the NHS with an extra £33.9bn a year by 2023-24 to support the long term plan and to make our health service fit for the future.”

Chris Hopson, the chief executive of NHS Providers, which represents hospital trusts in England, said: “The level of concern we’re hearing from frontline leaders about performance this winter is the highest we have known. The NHS is going in to winter in a much worse position than at any time in recent memory.

“We are short of capacity across the board – in mental health, ambulance and community services as well as hospital beds. And there has been another 12 months where social care and GP capacity has lagged well behind the growth in demand.

“The NHS has over 100,000 vacancies, so there was no respite over the summer and staff are now exhausted. On top of all this, we are losing serious amounts of vital senior clinical and leadership time because of current NHS pensions problems.”