NHS Connecting for Health believes that only a handful of patients have actually turned up to find that doctors were not expecting them. But as many as 340 are thought to have been given details of another patient's appointment by mistake.
It is likely that new referrals are also being affected because the cause is unknown.
Dr Richard Vautrey, deputy GPC chairman, warned that problems like this were denting GPs' enthusiasm for the new system.
‘As soon as Choose and Book shows that it's a reliable, robust and easy-to-use system, more GPs will use it,' he said.
‘Until then, practices will continue to make their own decision about it.'
Connecting for Health has delayed the release of version 4.0 of the Choose and Book system while it deals with the problem.
A spokesman admitted that turning up at an appointment where they are not expected would ‘clearly be confusing for patients', but stressed this was only happening in a tiny minority of cases.
Choose and Book makes 70,000 referrals a week.
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