Health leaders are being forced to draw up plans for NHS services that they do not think can be delivered, the head of the body representing NHS trusts has said.
Chris Hopson, chief executive of NHS Providers, told MPs on the Commons health committee that the financial requirements placed on sustainability and transformation plans (STPs) are leading to "vastly over-ambitious" proposals.
Trusts have also warned they can only meet the financial aims through "major structural service changes" to the NHS.
STPs are currently being drawn up in 44 areas of England.
NHS England has demanded the plans work locally, but tackle national commitments - including returning the NHS to financial balance, seven-day services, meeting targets for cancer treatment and focusing more on prevention of ill health.
Critics say they are a cover for cuts to services and could lead to the closure of hospitals or departments.
Mr Hopson told the committee that the "financial gap" in many STPs totals "hundreds of millions of pounds", and added: "They are now looking at a set of figures that to be frank just look completely undeliverable.
"Our members very clearly asked the question in June and July, 'Do you want a plan, any plan, that balances to that very reduced figure or do you want us to tell you how far we can get?'
"And the answer came back very clearly, 'You are not allowed to submit a plan that doesn't balance to the 2020-21 figure'.
"Our members are saying to us they are spending quite a lot of time creating plans that in their view are not deliverable and usually involve major structural service changes because that's the only way they can create a balanced plan.
"And our view is actually that really risks blowing up and destroying a process that actually seems to us to have a huge amount of fundamentally positive benefits. And that's a consistent story we're getting from virtually all of our members."
The Health Service Journal (HSJ) reported that he told MPs the plans are deemed overly ambitious because "they won't command the required political support and there isn't the capital available".
He stressed that trusts believe they can do more to deliver efficiencies, but want "realistic targets".