Health watchdogs are warning NHS managers that they must consult the public before going ahead with plans to close a mental health unit used by 3,500 patients a year.

Although Oxfordshire Mental Healthcare Trust wants to close the Isis Centre, in Little Clarendon Street, Oxford, the Patient and Public Involvement Forum is advising staff that they are legally bound to inform the public before making any changes.

Mental health managers have now said they will review their proposals, following an announcement by the PPIF yesterday that it was going to write to the trust's chief executive, Julie Waldron.

Members of Oxfordshire's joint health overview and scrutiny committee yesterday criticised the trust's lack of consultation on the plans and said they would support the PPIF.

The walk-in unit offers counselling and psychotherapy to a wide range of people - many of whom are seriously ill.

The unit is unusual because any treatment is not recorded on a patient's medical notes. But the trust wants to close it as part of cost-saving measures.

Mike Botting chief executive of the Oxfordshire and Area Consortium for Patient and Public Involvement in Health, which oversees the mental health PPIF, said the forum had written a "robust" letter to Ms Waldron.

He said: "There are statutory requirements for this trust to consult and the forum will tell them they must comply."

Protesters have criticised the trust's plans to close the Isis Centre, as well as its decision not to carry out a formal consultation.

In a report to yesterday's scrutiny committee, Jane Hanna chairman of the South Oxfordshire Mental Health Local Implementation Team, said: "If it closes in 2005, it will be a huge loss to clinicians and patients for a saving of only £30,000."

After the meeting, Ms Waldron said: "We are very concerned that there's a feeling that we didn't consult adequately on this issue. We were following the advice we were given at the time, and consulted users, carers and staff about the changes."