Andrew Lansley's health reforms face a fresh crisis as a powerful committee of MPs says the changes are obstructing efforts to make the NHS more efficient and that they fail to address the most urgent health challenge of modern times – how to care better for an expanding elderly population.

A highly critical report by the cross-party select committee on health, due to be published on Tuesday or Wednesday, comes as the medical establishment prepares to stage its own summit on Thursday to discuss concerns over the health and social care bill. The report, a late draft of which has been seen by the Observer, will cause alarm in Downing Street as it is the work of a committee with a Tory and Liberal Democrat majority and is chaired by Stephen Dorrell, a former Conservative health secretary.

One of its key messages is that Lansley's far-reaching attempts to restructure the NHS in England and devolve more power to GPs are making it more difficult to deliver on a separate target of £20bn of efficiency savings by 2014-15. The report echoes the widespread view in the medical profession that it is deeply unwise to be inflicting far reaching structural reform on the NHS at the same time as asking it to make huge savings.

The MPs say that instead of finding savings by innovation and greater efficiency, many hospitals and trusts are simply cutting services, despite Lansley's assurances that this would not happen. It says: "The reorganisation process continues to complicate the push for efficiency gains. Although it may have facilitated savings in some cases we heard that it more often creates disruption and distraction that hinders the ability of organisations to consider truly effective ways of reforming service delivery and releasing savings."

The report voices frustration that Lansley's plans fail to grasp the real challenge facing a cash-strapped NHS – that of moving more care into the community in order to provide better, more affordable and more integrated social and health services for the elderly. Members of the committee, including Dorrell, are known to be concerned at the rising cost to the NHS of caring for elderly patients, many of whom could be kept out of hospital if they were offered help to live at home or in the community.

Calling for a change of direction, the MPs say they found "precious little evidence of the urgency which it believes this issue demands – on both quality and efficiency grounds".

Last week the pressure on Lansley increased when official health department data revealed that the number of patients not being treated within the 18-week time limit has soared by 43% since the coalition took office. Thursday's meeting of all 20 members of the Academy of Medical Royal Colleges has been called by the British Medical Association, which, along with the nurses' and midwives' unions, wants the bill scrapped. The meeting comes as one of Downing Street's advisers on the NHS, Professor Chris Ham, King's Fund health thinktank chief executive, warns that growing disquiet across the medical establishment "could become an NHS version of the Arab spring".

The bill returns to the House of Lords next month.

Shadow health secretary Andy Burnham said: "The committee have delivered a damning verdict on Lansley's mishandling of the NHS. It is time for David Cameron to listen to what doctors, nurses and now his own senior MPs are saying and call a halt to this reckless reorganisation."

Ham said the MPs were right to warn that Lansley's reorganisation was stopping the NHS making necessary changes.

Health minister Simon Burns said: "We all know the NHS is facing pressures from an ageing population and the increasing costs of medicines. That's why we are spending an extra £12.5 billion on the NHS. If we are to put the NHS on a sustainable footing for the future reform is essential. Our modernisation plan will put doctors in charge, slash bureaucracy and give much more power to patients."