Foundation trusts could challenge the cap on earnings from private patients under EU law, the Foundation Trust Network has warned.

Responding to regulator Monitor's consultation the network has said some foundations view the cap as a "restraint of trade". Director Sue Slipman said she could not rule out the unnamed foundations challenging the cap using EU competition law. The cap limits the proportion of total income a foundation can earn through providing goods and services to private patients.

Unison launched a judicial review last year claiming Monitor interpreted the cap too leniently. Monitor allows trusts to disregard income earned through joint ventures or received via third parties.

Earlier this year Monitor persuaded the High Court to suspend Unison's challenge when it began a consultation on its own interpretation and two tighter alternatives, but the network response this week said even the current interpretation was "too restrictive". Ms Slipman said: "The other two options would enormously restrict things like innovation and joint ventures."

Extra income

The network's written response says the cap as it stands could hamper foundation trusts if the government sanctioned private top-ups or if the EU opened a free market in healthcare. The cap also limits their ability to offer a "quid pro quo" on-site extra income for NHS doctors.

The cap is limiting foundation trusts' ability to respond to the government's "health and wellness agenda" by providing services to local authorities and employers, the network claims. Ms Slipman said it wanted a separate debate about those areas. That could have a particular impact on mental health foundation trusts, which tend to have a cap set at or close to zero.

Unison issued a statement dismissing the idea: "Subjective analysis of what might benefit the NHS or assist the NHS's purposes should determine whether income [counts] towards the private patient income cap." Unison head of health Karen Jennings said had these new network proposals been argued at the time of legislation "foundation trusts would not exist".