Andrew Lansley's decision to downgrade the four-hour waiting target for accident and emergency admissions may have triggered the current beds crisis, an official NHS quango has concluded.

A report seen by The Independent on Sunday undermines the Government's position on the A&E crisis and will fuel calls for the target to be reinstated.

An emergency summit last month by the NHS Trust Development Authority (TDA), a quango that monitors the performance of hospitals, concluded that reducing the A&E waiting time target in 2010, from 98 per cent of people seen within the four-hour period to 95 per cent, may have had the "unintended consequence" of putting pressure on casualty departments.

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The downgrading of the target could have removed the priority of getting people seen within four hours, leading to delayed discharge of patients and a gradual build-up of queues, the report suggests.

Since the current crisis erupted two months ago, Jeremy Hunt, successor to Mr Lansley as Health Secretary, has insisted that Labour's decision in 2004 to allow GPs to opt out of offering round-the-clock care has been the main cause of the crisis, triggering a major political row.

But it is thought that the roll-out of the non-emergency-number 111 service has compounded existing pressures, such as staff shortages and an increasing elderly population suffering from a prolonged winter.

Now the TDA is pointing the finger at Mr Lansley, who was Health Secretary until last September and who faced widespread criticism for his radical reform of the NHS.

As one of his first acts as Health Secretary, in June 2010, Mr Lansley changed the target from 98 per cent of people seen within the four-hour period to 95 per cent.

A report of a board meeting on 23 May this year, called to examine the causes of the pressure on hospitals, says: "The reduction of the standard in 2010, from 98 per cent to 95 per cent, may have had the unintended consequence of removing priority from the A&E standard which has compounded in the three years since, resulting in the recent delivery issues."

The TDA also says the "dip in performance" in 2013 by A&E departments has been "more sustained than in previous years" due to the increasing numbers of elderly patients turning up at A&E, staffing shortages and the much-criticised 111 roll-out. Very few NHS hospitals see 98 per cent of patients within four hours.

At the height of the crisis in April, an average of 92.9 per cent of patients were seen in under four hours in England's largest accident and emergency departments. By the first week of May the situation had improved to just above the 95 per cent target.

Some 46 out of 60 NHS Trusts with "type 1" departments – those with 24-hour, consultant-led care – met the 95 per cent target in the first week of May, up from just over half, 34 trusts, at the crisis peak in April.

Andy Burnham, the shadow Health Secretary, said: "It is now clear that David Cameron and Jeremy Hunt have not been straight with people about the causes of the A&E crisis. Their public statements do not reflect what their own advisers have been telling them in private.

"After this revelation, David Cameron and Jeremy Hunt should have the decency to admit their own role in this mess instead of desperately trying to blame everyone but themselves for their A&E crisis."

A Department of Health spokesman said: "The public expect to have their medical needs met quickly and efficiently. Nowhere is this expectation higher than in A&E.

"What is essential for these patients is that they receive the best available care and that doctors get the time they need to treat them. This is why we decreased the standard of people being seen in A&E in four hours from 98 per cent to 95 per cent, to give doctors time to treat the patients who need complex care.

"We know A&E departments are under increasing pressure and we are working with the NHS to address the problems facing them now and in the future... Sir Bruce Keogh's urgent care review is looking at the range of pressures on emergency services and NHS England is making sure money is freed up and available to improve A&E services so that they are better able to cope next winter."

Miracle cure as Milton Keynes A&E goes from worst to best

Half past midnight, Milton Keynes Hospital, A&E. An ambulance pulls up bearing a concussed teenager; in the resuscitation room a man in his 40s comes round from a sleeping-pill overdose, and in the waiting room a dozen people cradle sprained limbs and sore heads.

"Late at night, agitation ripples like Chinese whispers through the waiting room," Jayne Skippen, the unit's formidable manager, tells me. On cue, a police car turns up. Officers accompany a woman who has cuts and bruises. At reception, she tells one of them to "fuck off" and she's back in the police car, under arrest for being drunk and disorderly. "She'll most likely be back in an hour or two," Jayne says.

So runs the stoic refrain of the doctors and nurses at Milton Keynes – everything comes back to A&E. This is the front line of an emergency care crisis which broke with the news that waiting times at A&Es hit a nine-year high in the first three months of this year. Milton Keynes was England's worst performer in 2012/13; it missed its target to keep waiting times below four hours for 95 per cent of patients by 10 percentage points. But in the past five weeks, however, it has become one of the country's best-performing A&Es.

The unit, which opened in 1984 with the capacity to care for 17,000 patients a year, in a catchment area of 130,000, has seen the local population more than double. It has become the place everyone comes to, for all manner of complaints.

Over the years the case load has shifted from "majors" such as cardiac arrests, to an almost 50:50 split with minors – anything from a sore arm to the vague complaints of patients staff call "frequent fliers". Then there are the drunks. "There are an awful lot of them, and they can be aggressive," says Lesley Willis, A&E receptionist for 29 years.

The hospital's new chief executive has a radical philosophy, which could be the reason for Milton Keynes's impressive improvement. "If [patients] feel hospitals are the place they want to come to for care then let's make sure that we have got the full range of urgent care, primary care and community care available for them at the front door."

It's that philosophy that lies behind a new unit which opened two months ago, and which was visited by Andy Burnham, the shadow Health Secretary, last Thursday. The ambulatory emergency care unit handles less serious patients and referrals from GPs during the day, leaving A&E with the serious cases.

The hospital aims to have a senior consultant in A&E until midnight, and "senior decision-makers" always available to advise more junior doctors whether to admit patients, or not, thus speeding up the process.

Better leadership and a sense of empowerment are galvanising the doctors and nurses, Jayne says. "Now I see fire in their bellies again."

At 1.30am, with things relatively calm, I leave. The doctors and nurses on shift won't be going home till around seven in the morning. Jayne has another mantra that sums up their attitude. Yes, everything may always come back to A&E, "but we'll just crack on".

Charlie Cooper