More than four million patients on NHS hospital waiting lists will be reassessed under a national review launched amid fears that health chiefs have prioritised coronavirus cases over the needs of all others – including advanced cancer cases.

NHS trusts will decide which cases should be seen within a month, two months, or left to anguish on their own at least three months, according to plans drawn up following warnings that too many patients have been left 'in limbo' after their treatment was put on hold.

While the programme is meant to speed up treatment for those in most dire need, millions assigned the lowest priority can expect to wait months, and in some cases years.

Patients will also be given the option to say they want to defer treatment for up to six months if they do not want to go to hospital during the coronavirus crisis – as officials had instructed until very recently.

The guidance states that the risk of delaying treatment should be weighed against the patient's health risks should they contract Covid-19, the need to self-isolate before surgey, and their reduced immunity afterwards, the Daily Telegraph reports.

Hospital staff are also being warned that patients, many of whom have already suffered long delays due to lockdowns, 'may become distressed or angry' when contacted.

It comes as MPs warned that failure to tackle a rising backlog could see tens of thousands of avoidable deaths this year, including up to 35,000 extra cancer deaths.

The Commons health committee heard that too many patients whose care had been delayed had been left 'in the lurch' without contact from hospitals – as a direct result of official policy to prioritise care for coronavirus patients.

Since the national lockdown imposed in March, the number of people forced to wait over a year for treatment has risen more than 50-fold, with 83, 203 waits in July compared with 1,613 in February.

However, nearly 75,000 people could die from non-Covid cases as a result of lockdown, devastating official figures buried in a 188-page document state.

The NHS guidance states: 'The project is about making the best mutually agreed decisions with patients and is not an exercise to reduce numbers on waiting lists.'

Those who decide to defer treatment would remain included in official statistics, it says.

Every patient waiting for planned treatment which involves hospital admission should be contacted before the review ends on October 23, for checks to ensure those in most urgent need are identified.

Hospitals which have already contacted patients on their waiting lists to review their condition have been told they do not have to repeat the exercise if their information is up-to-date.

Trusts will later be asked to carry out a similar process for millions more patients waiting for outpatients appointments.

An NHS spokesman said: 'The number of operations and procedures taking place has more than doubled since April, and to ensure that those with the most urgent needs are prioritised, specialists and their teams will be making contact with all those currently waiting for a non-urgent operation to discuss and assess their condition and preferences.'

Professor Neil Mortensen, President of Royal College of Surgeons of England, said the NHS review would help to ensure the most urgent cases are spotted.

He told the Telegraph: 'Surgeons and other clinicians across the NHS need to keep in touch with their patients to make sure they are not deteriorating while they wait for hospital treatment. If their needs become more urgent, they will be a priority for an early date for treatment.'

Liam O'Toole, chief executive of charity Versus Arthritis, added: 'It is imperative that any such review be open, transparent, and that patients and clinicians are fully involved in any decisions to their treatment that are made.'

It comes as an official document presented to the Government's Scientific Advisory Group for Emergencies (SAGE) warned that there could be 75,000 non-Covid deaths as a result of lockdown.

The startling research reveals that 16,000 people died as a result of the chaos in hospitals and care homes in March and April alone.

It estimates a further 26,000 will lose their lives within a year if people continue to stay away from A&E and the problems in social care persist.

And an additional 31,900 could die over the next five years as a result of missed cancer diagnoses, cancelled operations and the health impacts of a recession.

The estimates, drawn up by civil servants at the Department of Health, the Office for National Statistics and the Home Office, were presented to SAGE at a meeting on July 15. The documents stressed that had nothing been done to stop the spread of the virus in March, 400,000 people could have died of Covid.

And if the NHS had been overrun, this figure might have even soared to 1.4million. But they acknowledged the restrictions had significant unintended consequences.

The figures are bound to lead critics to ask why neither Health Secretary Matt Hancock or Home Secretary Priti Patel, whose officials compiled the report, has volunteered the information.

Both have spoken of the number of people who may die from Covid without stringent restrictions. But they have been less forthcoming about the risk that the measures themselves could lead to many non-Covid deaths, despite being made aware of the danger more than two months ago.

Many people took the 'stay at home' message to heart in the early days of the crisis, with hospital admissions plummeting as a result.

But despite fears in March that the NHS would be overwhelmed by a Covid surge, most hospitals were never overrun, and the emergency Nightingale hospitals set up in the spring remained empty.

The document said: 'We estimate changes to emergency care may account for 6,000 existing excess deaths in March and April 2020. If emergency care in hospitals continues to be low for a full 12 months, this could result in an additional 10,000 excess deaths.'

It added: 'We estimate there were approximately 10,000 non-Covid-19 excess deaths of care home residents in March and April 2020... there could be an additional 16,000 non-Covid-19 excess deaths over 12 months in care home residents.'

In the longer term, the officials estimate a 12,500 deaths over five years because of cancelled operations.

The impact on GP services could result in 1,400 deaths over five years from missed cancer diagnoses alone. The true impact will be much higher, they said, but they had been unable to model the impact on any disease area other than cancer.

The officials said lockdown will also lead to some reductions in mortality. Better air quality, fewer road accidents and less childhood disease will reduce overall deaths by roughly 1,000 over a year, they calculated.

And a further 4,000 lives will be saved thanks to 'healthier lifestyles in the short-term'. They estimated that 67,000 people will lose their lives directly from Covid across the UK by next March, although that figure was calculated before infections started rising again this month.

Added to the non-Covid deaths, the total death toll from the pandemic will reach 101,000 across the UK by next March, rising to nearly 150,000 in five years.

Finally, they warned of the devastation of a long-term economic downturn could lead to 18,000 excess deaths over two to five years.