If Peter Touche needed proof that his dream of a happy and carefree life with his twin sons and his American wife Laura had been ripped apart by incompetence at one of London's top private hospitals, it arrived on his doormat six months after her death.

The accountant had spent the weeks since Laura had died from a stroke following the birth of their sons at the Portland Hospital for Women and Children trying to seek an explanation from managers as to why his wife had not received treatment for two and a half hours while, unbeknown to nursing staff, her brain haemorrhaged after a caesarean section on 6 February 1999.

Instead, he received two letters that he found were demands for £800 each for the care of his sons – Alexander and Charles – while their mother lay critically ill.

In big red lettering, they read: "Notice of intention to issue legal proceedings.''

In the words of the grieving father: "It was a grotesque joke. Here was I trying to find out what had gone wrong and the hospital was sending me threatening bills. I didn't pay.''

Yesterday, after a three-year fight that saw Mr Touche, 33, lead his own legal battle through the High Court and change English law, a coroner's jury ruled that Laura's death had been contributed to by the neglect of the Portland.

Behind that ruling lies a story of clinical failure at a flagship hospital favoured by celebrity mothers from the Duchess of York to Victoria Beckham.

Speaking after the inquest verdict, Mr Touche said last night: "The facts that have emerged convince me that my wife's death was completely avoidable. The picture is far bleaker than I had imagined and the catalogue of errors is just unbelievable.''

Laura, 31, and her husband had chosen the Portland at a cost of £6,292 because "we believed we would get the very best in maternity care''.

On 5 February 1999, the former lawyer was admitted through the hospital's marble-coated reception centre where a doorman receives patients.

After a difficult labour had begun, a decision was taken that Laura should undergo a caesarean. Despite the emergency, the babies were born healthy and Laura was removed from the theatre.

It was then things started to go wrong.

The inquest, held at St Pancras coroner's court, in north London, heard how Laura, a descendant of two American presidents including Thomas Jefferson, was moved to a private room rather than a dedicated post-operative ward.

According to normal protocol in the NHS, Laura's blood pressure should have been checked every 20 minutes to protect against a brain haemorrhage. The Portland had no such protocol.

Between 11pm and 1.45am, Laura's medical charts are a blank – the result, the inquest jury was told, of a lack of "basic nursing care'' by midwife Grace Bartholomew.

At some stage after the birth Laura suffered bleeding in her brain, but such was the level of monitoring that her name had not even been written on a board to alert staff as to which patients were present.

The inquest heard that even when Laura's high blood pressure was detected, the necessary drug was not administered for at least 15 minutes because a doctor was locked in conversation with the consultant obstetrician and the medication was not available on the ward.

The first indication that there was something wrong came at 3am, four hours after the operation, when a midwife responded to an alarm. Fiona Laird said she found that Laura was "very ill".

"She told me she felt terrible and had the worst headache she had ever had," Ms Laird said. "Every time she lifted her head she vomited."

The alarm had been sounded by midwife Lottie Bowen-Wright after she found out about Laura's high blood pressure and headache.

"She said 'Don't leave me'," Miss Bowen-Wright testified. "Her head was very hot. I was talking to her, reassuring her. She was clinging to my hands."

Miss Bowen-Wright had replaced Grace Bartholomew, who had left Laura despite her complaints about a headache.

Laura was given an anti-emetic drug and another treatment to bring down blood pressure. But by the time her husband arrived, she was incoherent and suffering from fits.

She was rushed to an NHS hospital but died nine days later, her brain irreparably damaged.

The Touches had married in December 1996. Peter, the great-grandson of the founder of the Deloitte Touche accountancy firm, was a film finance executive, and Laura, a blonde east-coast American, had swapped a career as a lawyer to join the environmental policy unit at Kew Gardens. They lived in select Chelsea.

Suddenly Peter and his in-laws – Laura's parents Tom Coolidge, 67, and Susan, 61, and her sister Anne, 32 – found themselves with a terrible tragedy and a struggle to find out what had happened at a hospital whose reaction, they allege, ranged from the ill-mannered to the dishonest.

Mr Touche yesterday described a meeting on Valentine's Day 1999 with two Portland consultants 48 hours before Laura's life-support machine switched off.

Peter said: "When my wife was lying in an intensive care ward in the last hours of her life, they completely omitted to tell me that she had not been monitored for that crucial two-and-a-half hour period. I had to find out for myself. They even suggested her condition was from something congenital.''

After a fight through the High Court last year to force an inquest, something not previously required through English law, Laura's relatives were sent the notes of a meeting at the hospital about her treatment.

''At an internal meeting,'' Mr Touche said, "the hospital concluded that everything that could have been done was done. Had they conducted a full internal inquiry and made their findings known to me, we probably wouldn't have needed to be here today. I can only describe it as an attempt at a cover-up.''

Sat alongside his son-in-law, Laura's father – a descendant of the US president Calvin Coolidge – said he had been astonished at the level of care.

He said: "It took us almost three years to get the true facts. Legislation should be brought forward to ensure standards n private hospitals.''

Mr Touche, who describes his twin sons, now nearly three, as "real livewires, like their mother'', said the inquest verdict would at last allow him to get on with his life.

The accountant told reporters he had instructed his solicitors to write to the governing body for nursing in Britain, the United Kingdom Central Council for Nursing, Midwifery and Health Visiting (UKCC) – asking for Grace Bartholomew to be struck off.

Mr Touche's eyes briefly welled up when he was asked what he would say to the midwife if he met her. He said: " I would have nothing to say... except that I hope she isn't working anywhere else.''