A key part of the NHS information strategy is not millennium-proof even though it was built less than five years ago, according to a report for the NHS Executive.
The NHSnet electronic messaging service, launched in 1995, is going through a major programme of repairs to make it millennium-compliant.
Main contractor Syntegra claims the works should be finished in time for a full-scale test in July.
But the report, by Secta Consulting, recommends that the network should be regarded as 'at medium risk' until Syntegra declares its position.
A Syntegra spokesperson said: 'It is a big system with lots of components, many of them bought in. One would not have expected all the year 2000 issues to have been anticipated when the system was designed.'
NHS planning director Alas-dair Liddell announced this week that the executive will commission an independent review of NHSnet 'in the light of published reports of operational difficulties'.
Syntegra did not admit the extent of the year 2000 problems until last September, when health marketing manager Richard Harris wrote to the executive saying an extensive programme of upgrade and testing was required.
Several major components, including the main message store, the secure gateway and the Internet gateway, have since been swapped, and others still have to be modified.
Syntegra is also withdrawing one component of the messaging system, Kermit, forcing some trusts to buy new equipment to stay connected.
The company says it is impossible to make Kermit millennium- compliant, though rival messaging service Racal Healthlink says it will continue to support it.
Last week, compliance information on Sytegra's equipment was unavailable on the NHS's Y2K website, on which the majority of equipment suppliers have supplied detailed statements of their year 2000 status.
'To the best of our knowledge we are on schedule for dealing with these issues,' the spokesperson said.
But he refused to give firm dates for compliance, adding that the company avoids the word 'compliance' because of its legal implications.
Nor will the company disclose how much the year 2000 repairs will cost, or who will pay.
A statement issued on behalf of Tony King, director of the NHS Executive's telecommunications branch, denied that the NHS was contributing to the repair bill.
'The contract is for a managed service against a required performance level.
We would expect contract improvements to meet demand and technology advancements ensuring that the NHS does not bear such costs.'
Trusts have already complained of Syntegra's record on millennium upgrades.
The company's Clearnet systems, which many trusts use to transmit contracting data to health authorities, are known not to be year 2000-compliant.
The company is charging£2,000 for replacements.
None of the other major Clearnet equipment suppliers are charging their customers, according to the Secta report.
'This could potentially cost the NHS a significant amount and it really needs to be sorted out,' said author Chris Shovelton.