Doctors will not know the identity of the mystery patients

People who take part give their opinion on the standard of care they receive, but NHS staff do not know which patients are signed up to the project.

Clwyd Community Health Council is leading the scheme which will initially run for two years.

Conwy and Denbighshire NHS Trust said it would give all patients the opportunity to join the initiative.

Health Minister Brian Gibbons will officially launch the project on Tuesday afternoon at Ysbyty Glan Clwyd in Bodelwyddan.

They're just given a number so it's anonymous and staff will not know they are mystery patients Project leader Jean Mead

The scheme was already being advertised in waiting rooms, project leader Jean Mead said.

She told the BBC News website: "People seem quite enthusiastic about it. The leaflets have gone out in the last few days and we've already had a few responses from that."

Ms Mead, from the Clwyd Community Health Council, said the names of patients who participated would not be disclosed.

"We are independent of the NHS but we work closely with the trust," she said.

"Every time they [patients] go to hospital they fill in a questionnaire. They're just given a number so it's anonymous and staff will not know they are mystery patients," she added.

The council will submit a report to the NHS after two years, but will also feed back results to the trust during the course of the experiment.

The idea was also tried in Flintshire in 2002.

Ms Mead said that Conwy and Denbighshire NHS Trust were "particularly keen on public and patient involvement in the trust".

"It's an opportunity to find out what is not working well - and what is," she added.

The mystery patients will be sent tick-box forms so they can comment on the service they receive.

Participants can complete a form each time they use a clinic, hospital or other facility provided by the trust.

They trust said the feedback would help make "real improvements to services that will make the patient's experience that much better".