Hospital bosses in Bradford must put in place an action plan to improve maternity services after being ranked as one of the poorest performing units in the North of England.

The damning indictment comes from independent health watchdog the Healthcare Commission which today published the results of its national review of NHS maternity services, ranking the best and least well performing services in the country.

Bradford Teaching Hospitals NHS Foundation Trust, which manages the maternity unit at Bradford Royal Infirmary, was one of only two trusts in the North of England ranked in the bottom 21 per cent in the country, being rated "least well performing".

Earlier in the week, hospital bosses questioned the whole way the survey had been put together.

And today they hit back, saying the review did not paint an accurate picture of local services and the poor rating was linked to "problems with the way the Commission has been able to collect and use data". "In Bradford we were unable to provide some of the data required by the Healthcare Commission and this resulted in a lower score," said a spokesman.

Airedale NHS Trust, which runs the maternity unit at Airedale Hospital near Steeton, was given the second highest rating of "better performing" for its services.

The maternity unit at Calderdale and Huddersfield NHS Foundation Trust was given the highest rank of "best performing" and Leeds Teaching Hospitals was ranked as "fair performing".

The review took into account 25 factors - including staffing levels, numbers of midwives and consultants, the mothers' own views about delivery suites and the welfare of mothers and babies. The review covered the care provided from the time when pregnant women first accessed maternity services to their sign-off by the midwife.

Airedale received very high scores across the board and Kath Walsh, head of midwifery at the Trust, said: "We are very pleased that our maternity services have again been recognised for their high quality. Our staff are committed to giving the best care possible"

In Bradford, Professor Derek Tuffnell, consultant obstetrician and director of women's and children's services, moved to reassure people they could have complete confidence in the safety and quality of BRI's maternity unit, which sees 6,000 babies born every year.

He said: "We have a low caesarean rate and a high normal birth rate, offer midwife-led care and have an excellent neonatal unit.

"We also have phase three UNICEF Baby Friendly' status, which means we offer excellent support for breastfeeding. We have invested in an excellent new transitional-care unit that helps mums stay with babies who need extra care and have opened a purposely designed and redecorated delivery suite assessment unit, which helps provide support to mums-to-be. We know we have highly skilled, well trained staff, who work hard to provide care for women in pregnancy."

Professor John Wright, director of the Bradford Institute for Health Research, added: "The most important goal in measuring the quality of health services is to make sure that the measurements used are accurate and true. The conclusion of this review is undermined by limitations in the data used."

Anna Walker, the Healthcare Commission's chief executive, said: "Being put in the least well performing category does not mean that a service is unsafe. If we believed any unit to be unsafe, we would take immediate action to ensure patients were protected. Those trusts that were least-well performing should as a matter of urgency take steps to improve and we shall be checking that they do so. One reason some trusts performed poorly is because they did not supply the full data."