Rose Gibb, the former chief executive who received a £75,000 pay-off after presiding over a fatal infection outbreak, was prepared to 'stay and face the music', according to her trade union. She is suing her former employer for a further £175,000 plus interest, claiming she was forced to leave.

Ms Gibb stepped down at Maidstone and Tunbridge Wells trust days before publication of a report linking poor hygiene at the trust to the deaths of 90 patients from C difficile.

Jon Restell, chief executive of trade union Managers in Partnership, said: "The NHS told her she had no choice but to leave and so she accepted an offer of money to go.

"She was prepared to stay and face the music. It was her employer's decision to avoid any disciplinary action against her."

Mr Restell said the trust is contractually obliged to pay£250,000 under a compromise agreement. He said the trust is claiming the agreement was made ultra vires and is therefore not binding. "All of us, including the MiP's solicitors, who act for Rose, have been given no further explanation as to why the trust believes the agreement was ultra vires."

Maidstone and Tunbridge Wells has "failed" to resolve the dispute by negotiation, leaving Ms Gibb with "no choice" but to take the matter to the High Court, he added.

Last November, a month after Ms Gibb resigned, health secretary Alan Johnson halted her original severance pay deal and ordered a review.

The revised figure of£75,000, agreed by the trust in January, amounted to half her annual salary.