The Department of Health has raised concerns that Monitor’s definition of the private patient income cap “permits foundations and their advisers to adopt artificial structures to circumvent the cap”.

The statement was made in a “skeleton argument” submitted to the High Court by the DH for a judicial review this week of the foundation trust regulator’s interpretation of the private patient income cap.

Trade union Unison brought the judicial review, claiming Monitor has used “too narrow” a definition of “private income”, allowing foundations to extend the proportion of income earned from these patients beyond that intended by law.

In the High Court this week, Monitor defended its interpretation of the cap.

The health secretary, an “interested party” in the case, has attempted to push for an “intermediate” interpretation between Monitor’s and Unison’s, pending a fundamental review of the law on which the cap is based. The DH submitted a revised definition of the cap to the court.

The hearing, which continued as HSJ went to press, has centred on the meaning of the 2006 Health Act, which set a limit on the proportion of their income foundation trusts could earn from private patients.

Until earlier this year, Monitor interpreted the law to exclude income from charges levied by third parties and income derived through joint ventures and so-called associates. Unison has argued it should be much wider and include all income, however derived, from private patients.

Earlier this year Monitor tightened its interpretation to include joint ventures and associates but both Unison and the DH told the court it was still “unlawfully narrow”.

Monitor argues that, as the independent regulator, it is at liberty to define the cap as it sees appropriate and in keeping with its other statutory duties.

Unison has asked the court to quash every financial reporting manual Monitor has issued since 2006-07 and declare them “unlawful”.

Monitor has argued there is no legal basis for such a “retrospective unravelling” of the guidance.