The independent sector is still struggling to provide good quality data on its NHS activities, the NHS Information Centre has revealed.

Its latest report - covering April to December 2007 - reveals significant problems with the data provided by 23 independent sector treatment centres and 11 other independent providers to the NHS.

Providers were not able to state the ethnic origin of 60 per cent of patients and a primary diagnosis for half. Data quality on the decision to admit was also poor, affecting the ability to report on 18-week referral to treatment times.

The report says: "With the introduction of free choice contracts, it is important that the data is accurate for payment and purposes to support patients in informing their choice of provider."

Martin Orton, strategic adviser to the centre, said there had been improvement on last year but admitted that the data quality was not good enough. "But you could say that about the NHS too," he added.

The report also reveals wide disparities between providers, with some able to provide highly accurate data and others struggling.

Spire Healthcare is consistently highlighted for its poor performance. A spokesperson said: "We recognise that our performance in this area is unsatisfactory and we have been working closely with the Information Centre to rectify this."

A DH spokesperson said: "Failure to comply with data reporting requirements could lead to sanctions under the contract for providers.

"The department expects the independent sector to provide high quality and timely information including the key NHS datasets. The department actively monitors CDS [commissioning datasets] data quality from ISTC providers and is working with the Information Centre and providers to continuously improve data quality."