The "deeply flawed" decision to downgrade several North West London hospitals must be halted, according to a report by Michael Mansfield QC.
It warns the closures threaten "the fundamental principles of a universal NHS".
Waiting times at local A&E departments increased sharply after those at Hammersmith and Central Middlesex Hospitals were closed.
The report says the reorganisation had no "up-to-date business plan".
Consultation was inadequate and departments had been shut without providing adequate alternative healthcare, it added.
It said: "Overwhelmed and inconsistent" GP services are "clearly failing to meet demand across the region".
But a spokeswoman for NHS London said patients now had better access to GPs and that more A&E consultants and nurses had been recruited.
The Independent Healthcare Commission for North West London, led by Michael Mansfield QC, found the 'Shaping a Healthier Future' (SaHF) plan would cost at least £1bn, with "spiralling management and consultancy costs".
Cutbacks had been aimed at the most deprived communities, and many vulnerable patients were now forced to travel to hospitals with poor public transport links.
The commission was particularly concerned about plans to close the "exemplary" maternity unit at Ealing Hospital.
The SaHF programme had failed to consider the fast-growing population of North West London and the rise in the number of over-60s.
It had sought to save money in anticipation of NHS cuts that had not transpired.
The report's recommendations
•The decision to close Ealing maternity unit should be reversed immediately
•Reopen the A&E department at Central Middlesex Hospital
•The National Audit Office should undertake a review of the programme's value for money
•A new public consultation is needed as the proposals have changed significantly
•Substantial investment should be made in GP and out-of-hospital services
.•Ealing and Charing Cross hospitals must retain full 'blue light' A&E services for the foreseeable future
The plan aimed to redirect patients to Urgent Care Centres, but the commission said there was "widespread confusion" among GPs, consultants and patients about what the centres could do and who should go there.
It said they should be co-located with A&E departments wherever possible to avoid "fatal consequences".
NHS London defended the plan, saying patients were already benefitting from it.
"We now have eleven community hubs open across North West London, which provide a range of health and social care services in one place, closer to people's homes.
"Part of the improvement plan includes additional investment to modernise and increase capacity in our hospitals and community sites."