The telephone helpline NHS Direct is helping fewer patients than expected to treatthemselves rather than consult a GP, and has increased the financial burden on the NHS, a survey has found.

Fewer than one in five callers to the nurse-led service changed their plans to consult a GP as a result of the advice they received. The demand on accident and emergency departments and the ambulance service is unchanged.

Calls to GPs' out-of-hours services are also unchanged, although the researchers said the rise in these calls had been halted since NHS Direct was introduced.

The limited impact on patient demands was revealed in a survey published yesterday at a conference marking NHS Direct's second anniversary. However, the research by the University of Sheffield showed the service was popular with patients, with 90 per cent satisfied with the advice given.

NHS Direct is an important factor in the Government's strategy to modernise the NHS, promising easier and faster access to medical advice. Early evidence suggests it has achieved this aim, but it has so far failed to curb the increasing demand for care. In its first two years it cost £66m, and next year the annual budget will rise to £70m.

The announcement yesterday that the least urgent calls to the emergency 999 service will be routed to NHS Direct in a trial scheme in five pilot areas was a sign of government anxiety about its lack of impact. Gisela Stuart, Health minister, told the conference, organised by the Royal College of Nursing (RCN): "I strongly believe there is a major scope for NHS Direct to help take the pressure off ambulance services."

After its launch, initial surveys of the service's first three pilot areas suggested that 40 per cent of callers were being diverted from consulting GPs and accepting advice such as to go to bed with a hot drink.

However, the latest surveyshows that, of the callers who first said they intended to contact their GP, only 18 per cent were advised that they did not need to, less than half the earlier finding.

A spokeswoman for the British Medical Association (BMA) said yesterday: "NHS Direct could provide a useful additional service, but on the present evidence it is not going to be a replacement service."

Doctors have criticised the service on the grounds that it was being rolled out too fast before being evaluated. Last week GPs clashed with the Prime Minister at a BMA conference, with some saying the resources invested in NHS Direct might have brought a greater gain had they been invested in general practice.

Elsewhere enthusiasm for NHS Direct is running high. Christine Hancock, RCN general secretary, told the conference it was an "extraordinary achievement" and was "transforming health care".

NHS Direct now covers 60 per cent of England. It is scheduled to be extended to the rest of England by October, and to Wales by the end of the year. Services for Scotland and Northern Ireland will follow.