The breast screening unit auditing over 100,000 files of past patients did not have an adequate system to detect clerical errors, and is one of the only units in the country not to employ a superintendent radiographer to oversee its mammography service.

As revealed by HSJ last month, the unit at Charing Cross Hospital, part of Hammersmith Hospitals trust's imaging department, is reviewing files for clerical errors, following the detection of a recall error in one patient's file.

The regional breast screening quality assurance unit was notified and external auditors PriceWaterhouseCoopers were called in to review all files dating back to 1993. The£200,000 investigation is likely to take about six weeks.

However, experts have told HSJ that the error - which involved the patient's file being put in the wrong pile - should not have occurred as all units are required to have systems, computerised or manual, in place that are able to prevent mistakes.

Dr Robin Wilson, clinical director of the breast unit at Nottingham City Hospital, said: 'There is supposed to be a failsafe mechanism in place, and there was a directive from the national screening office a few years ago about this. ' He also said that it would be expected that each breast screening programme should have a superintendent radiographer.

He said the lack of a superintendent would worry him 'because the quality of mammography is fundamental to screening and requires major input'.

Gill Beeton, who was superintendent radiographer at Charing Cross until the post was axed last May, said the decision to remove the post was a shock to staff.

She said: 'There are one or two units that have tried not to have one, and have hired one again later. ' She added that the unit is now 'lacking quality, employed mammographers and therefore morale is low'.

Senior radiographer Fiona Egan, who was Ms Beeton's deputy and left the unit in October, described the unIt is problems in her exit interview.

She said: 'I told them that I didn't like the management and that the quality of breast screening was suffering. '

Royal College of Radiologists breast group chair Dr John Fielding said: 'It would be an unusual situation for anyone else to be able to run a service and I personally can't see how you could do it satisfactorily. '

A spokesperson for the trust said the decision to replace the superintendent post with a nurse manager post had been made after a regional quality assurance audit had called for a rationalisation of lines of communication within the department.

Although there is a shortage of qualified radiographers nationally, the unit is understood to suffer from particular recruitment problems and to employ a high number of agency staff, though the trust spokesperson said staffing problems were no worse than elsewhere. Within the last few weeks, screening work was compromised when the wrong film was used during a day's work.

The trust says the error was discovered during the morning and the images were still usable.

However, HSJ has been told the problem arose because of the large number of junior, locum staff used in the unit.