When is a patient not a patient? When he is a "client" or "service user", according to one NHS trust.

Staff at Sussex Partnership NHS Trust, which came into existence at the beginning of this month, have been ordered not to describe some patients as patients.

They have been told to refer only to those in hospital as patients; everyone else should be called "clients" or "people who use our services".

The order was made by Lisa Rodrigues, chief executive of the new trust.

The trust is responsible for mental health, learning difficulty and addiction services across the county, covering a population of about 1.5 million.

In a report to the board under the heading Language and Accessibility, Ms Rodrigues said: "People who are in our hospitals are patients. Otherwise we refer to our clients as people who use our services."

A trust spokesman said the decision was made so that people who are treated in the community would not feel stigmatised.

He said: "One of the issues of the field of mental health is what language to use.

"People in hospital are patients and people outside the hospital are called clients and it has been used for years.

"Political correctness is somewhere you have to go to protect vulnerable people."

In the same report, Ms Rodrigues tells staff to beware of acronyms and jargon that may be useful to those who understand them but exclude partners and act as a barrier to understanding by the public.

She also states when and when not to use capital letters and says no report should cover more than two sides of paper.

The new trust has about 4,500 staff.

It was formed following the merger of East Sussex County Healthcare and West Sussex Health and Social Care NHS Trusts.

It has also taken over the running of mental health, addiction and learning disability services in Brighton and Hove from South Downs Health NHS Trust.

Speaking at the launch of the trust earlier this month, Ms Rodrigues said her aim was to provide the best service possible for people in the county.

She said: "We have brought together services from three organisations.

"With the new Sussex Partnership we can speak up for mental health, learning disability and addiction services.

"We will challenge discrimination and promote inclusion.

"We will provide services to the highest modern standards of care and introduce new specialist services that until now have not been available in this area."

Commenting on the order, a spokesman for the Campaign Against Political Correctness said: "I would be very surprised if people felt stigmatised by the word patients'.

"Once again we are seeing the rewriting of language, which is part and parcel of political correctness."