Heather Heslop has been writing back and forth to health chiefs for more than 11 years to find out how her son died. She refuses to accept the hospital's explanation.

In her front room in Diss, Heather Heslop has file after file about the death of her son.

The paperwork contains copies of letters she has written to the Norfolk and Norwich University Hospital (N&N) and their replies spanning more than 10 years. Since her son Jonathan died in 2004 aged 39, from septicaemia, Mrs Heslop has been trying to find out why he was given a drug which he was allergic to.

An investigation in 2008 into Jonathan's death found no clinical negligence in his treatment. The N&N said Mrs Heslop's complaint has been thoroughly examined and 'detailed' replies sent to her.

Jonathan's medical records show he was given a drug called phenytoin, which he was allergic to, before his death. Why and how he was given that drug, are questions the hospital has not answered, Mrs Heslop claimed.

Among her files, Mrs Heslop has dozens of replies from the N&N to her letters. Those letters begin in 2005 and state the hospital had taken 'careful note' of her complaint.

But they go on to explain that Jonathan did not comply with his treatment which was 'fundamentally the problem'.

In the hospital's latest response to widowed Mrs Heslop just before Christmas this year, the N&N said it would not be sensible to re-investigate the death after so many years.

'We have provided detailed explanations to Mrs Heslop's queries and her son's death was extensively investigated, both internally and externally,' a hospital spokesperson said.

'Mr Heslop had a complex medical history with a number of serious long-standing medical conditions.

'Mrs Heslop's questions were looked into and detailed replies provided in writing and in person.'

Mrs Heslop contacted the EDP about her son's case after reading an article in this newspaper at the end of November about the N&N.

Mr Heslop was admitted to the N&N in 2003.

His medical notes from the ward at the time recorded phenytoin on his drug allergy chart.

But when he died in 2004 on a different ward, his medical notes made no mention of the drug allergy.

Phenytoin is used to treat seizures, but in rare cases allergic reactions to phenytoin can result in damage to the liver or bone marrow.

The death of her son was not referred to the coroner in 2004, but in 2008 Mrs Heslop's letter writing paid off. She contacted Norfolk's coroner and an independent, external review was carried out by a Professor Tattersall into the case and his mother's questions.

The review found that the death was due to 'natural causes' and there was 'no suggestion of negligence on the part of medical or nursing staff'.

Jonathan died from septicaemia but Mrs Heslop said none of the investigations, letters or reports answer her grievance around Jonathan being given phenytoin.

'Questions that I want answers to have been ignored,' Mrs Heslop said. 'I have nothing without my son. I want them to apologise and then I may go away.'