A computer database containing potentially vital information on the Bristol heart scandal has been stolen, a public inquiry has been told.

Health officials do not know anything about how the files, compiled by cardiac specialists over a three-year period, went missing from the hospital trust at the centre of the scandal.

BBC West's health correspondent Matthew Hill, who helped uncover the story, says the missing files could contain vital evidence for the inquiry, which began on Tuesday and is expected to last 18 months.

The inquiry was told that the missing files together with the chaotic record-keeping system at the hospital made it difficult to draw accurate conclusions about procedures.

Also revealed was the fact that doctors had written to deny there was a problem with child heart surgery at Bristol Royal Infirmary (BRI) as far back as 1987.

This was in response to a BBC Wales documentary.

The doctors said heart surgery was equal if not better at BRI than at most other paediatric units.

The inquiry was set up after a General Medical Council hearing which found three doctors guilty of serious professional misconduct.

Two were banned from practising and another was censured.

The GMC investigated the deaths of 29 children and brain damage suffered by four others in connection with heart operations between 1988 and 1995.

Campaigning parents say many more children died or suffered brain damage following complex heart surgery at the hospital.

'Thrilled to bits'

On Tuesday, the inquiry, which was packed with bereaved parents, heard from Tracey Clarke, whose daughter Melissa died after a failed heart operation in 1991.

Melissa was declared brain dead after her ventilator failed following the operation to switch her arteries.

Mrs Clarke had asked for the ventilator to be turned off so she could hold her baby in her arms.

But she broke down as she told how she was denied that chance and Melissa died in a nurse's arms.

Tracey Clarke: broke down as she gave evidence

Mrs Clarke said she was told by BRI doctors that Melissa would be fine and that the "routine" operation had a 95% success rate.

She said she was "thrilled to bits" when Melissa was transferred from Exeter to BRI after developing heart problems soon after she was born.

"I had no reason to doubt Bristol and I just assumed she was in the best hands," said Mrs Clarke, who is one of around 100 parents planning to sue the Infirmary.

Twenty-eight cases are believed to have been settled by the United Bristol Healthcare Trust (UBHT) which runs the BRI.

Mrs Clarke also told how she had only learnt three weeks ago that Melissa's heart had been retained following a post-mortem.

She had thought the heart was returned when Melissa was cremated and said she found the news "very distressing".

Opening with a clean sheet

Brian Langstaff QC said the inquiry - the biggest ever investigation into NHS care - had "many questions to ask, but as yet no answers".

He stressed the proceedings were not a trial and added that he hoped that the evidence would enable parents to find out " whether there was anything they might reasonably have done which could have secured a better outcome."

He confirmed that the inquiry, which is expected to cost �15m and investigate more than 2,000 operations over a 12-year period, would be much broader than the GMC's investigation.

"This inquiry will be the widest ranging examination ever of the NHS conducted independently," he said.

Among those in attendance were Hugh Ross, chief executive of the UBHT and members of the Bristol Children's Heart Action Group, which represents 250 families whose children died.

Also present were members of the Bristol Surgeons Support Group.

This group represents 500 families who want to restore the reputation of the three doctors.

Mr Langstaff said: "We start this inquiry with a clean sheet. At this stage there are no answers, merely questions."

Professor Ian Kennedy will head up the inquiry

The inquiry's chairman, Professor Ian Kennedy, has promised it will be as open as possible.

Live transmissions of the evidence will be beamed into community health centres in Barnstaple, Taunton and Cardiff.

Would-be contributers can send evidence in using e-mail and a phoneline.

At the end of each day's proceedings, a transcript of evidence will appear on the inquiry's website.