A family's appeal for a bone marrow donor has left the National Blood Authority struggling with a backlog of 3,000 unchecked blood samples.

Thousands of people joined the British bone marrow registry after the parents of Molly-Ann Barnett, of Hessle, near Hull, appealed for help in finding a donor for the six-year-old, who has leukaemia.

Last year, the NBA tissue-typed 5,000 samples, and its target for this year is 10,000.But although it is 'ahead of target', the Molly-Ann appeal has left it with 3,000 samples unchecked.

Spokesman Jim Moir said: 'Normally in a session in North Yorkshire we would get 120-150 blood donors.

'In some sessions (after the appeal) we were getting 200 to 250. People were sitting in queues for hours.'

He added that the NBA was working with Molly-Ann's family to manage the flow of donors. 'We understand that the parents must be desperate but it is managing the process, 'he added.

Molly-Ann's father, Paul Barnett, has written to prime minister Tony Blair calling for an overhaul of the bone marrow registry system and accusing the government of 'failing' people trying to help his daughter.

The NBA has improved its activity from processing 75 samples a week to 200, and expects to reach 400-500 a week within the next few months.

The Anthony Nolan Bone Marrow Trust runs the main register for bone marrow donors in the UK.

HSJ understands it told Molly-Ann's family it can only cope with 350 new people a week, but the family went to the NBA instead.

A spokesperson for the trust said there was a need for additional resources to meet demand.

It needs£10m a year to operate at its present level of recruiting 350 new donors a week, and doing further tests on possible matches.

'It is not just money, ' the spokesperson added. 'We are talking about laboratory space, scientists and equipment.'