NHS Direct, the 24-hour healthcare telephone helpline, is not being used by the groups who need it most and is failing to meet performance targets, the National Audit Office says in a study today.

It discovered that the poor, the elderly, young people, the disabled and those from ethnic minorities were not keen to use the service, which costs £99m a year. Although NHS Direct had a high level of customer satisfaction, one in five callers had to wait more than 30 minutes for a nurse to call back. Last September only 64 per cent of callers managed to speak to a nurse within five minutes, compared with a government target of 90 per cent.

The audit office said NHS Direct needed to develop a clear strategic staffing plan to ensure its expansion did not take nurses from other parts of the health service.

In its report to Parliament, the financial watchdog said the service should be praised for its successful launch. The 24-hour helpline is staffed by call handlers who put inquiries straight through to a trained nurse or get them to ring a patient back. It is the world's largest provider of telephone health care, receiving 3.5 million calls in 2000-01, with projections for 6 million calls in this financial year.

The service aims to relieve pressure on GPs and hospitals by advising on care, frequently resulting in patients treating themselves. Nearly half of the running costs of NHS Direct were met from savings to the rest of the health service.

But the audit office said little more than half of pensioners and the 15-24 age group knew of the service. Of the very poorest, social groups D and E, 49 per cent were aware of the helpline. It said: "These groups had as much need as others of the service, and perhaps an even greater one."

The report doubted whether the target of 90 per cent of callers speaking to a nurse within five minutes would be met. It said NHS Direct was changing the target waiting time to 20 minutes.

Sir John Bourn, head of the the audit office, said it was a significant achievement to get the service running in less than three years but there were causes for concern. "It should address the fact that some social groups are tending not to use the service, and increase the proportion of callers who are promptly connected to a nurse," he said.

Edward Leigh, Tory MP and chairman of the Commons Public Accounts Committee, which oversees the audit office, said: "Clearly, greater effort must be made to reach these groups. And service standards are wanting when a fifth of callers have to endure a wait of more than 30 minutes."