London’s hospital trusts are being told to plan their future in a significantly smaller acute sector - or have it dictated to them.

Primary care trusts in each area of the capital are developing plans understood to include merging trusts or having them acquired by foundations, as well as reconfiguring services.

The plans are not being published until formal consultation is carried out. This should happen late this year or early next, but raises the prospect of political challenges in the run-up to a general election.

Trusts without foundation status in the north west, north east, north central and south west of the capital are most likely to be affected. Three trusts in south east London were merged earlier this year.

Westminster PCT chief executive Michael Scott, who is leading plans in the north west, said it had set out “options but not conclusions” for trusts, which they had to respond to. He said: “If people can’t come up with plans on their own [to be sustainable]… we are going to have to engineer a solution.”

Likely options are merger with community service providers, which Ealing trust is considering, mergers of acute trusts, or being acquired by a foundation trust.

At the same time PCTs are deciding whether to pay off the historic debts of London trusts with the worst financial problems. They will only do so if trusts have viable plans, which in turn depends on the sector proposals. So far, the PCTs have refused to pay the debt of Barnet and Chase Farm Hospitals, North West London Hospitals, Whipps Cross University Hospital and West Middlesex University Hospital trusts.

Wandsworth PCT chief executive Ann Radmore, who leads the London Challenged Trust Board, said acute board chairs “have been asked some difficult questions and have had to go away and think”.

Barnet and Chase Farm Hospitals said its “starting point” was the controversial reconfiguration plan it consulted on last year. North West London Hospitals said, provided it developed a viable strategy, it would prefer to remain a standalone trust.

West Middlesex is working with NHS Hounslow to “develop a mutual understanding of the range and size of services to be provided”, while also “exploring opportunities for joint working with other healthcare providers”. Whipps Cross could not be reached for comment.