London Ambulance Service has admitted a catalogue of errors after a delayed 999 response left a woman brain damaged.
Caren Paterson, 33, collapsed and suffered brain injuries after waiting more than 90 minutes for an ambulance crew waiting about 100 metres away.
Paramedics were ordered not to enter her flat in Islington without a police escort as it was graded high risk.
The ambulance service admitted 11 breaches of duty that contributed to Ms Paterson's injuries in 2007.
Ms Paterson is claiming compensation against London Ambulance Service (LAS).
The 11 breaches included failing to comply with hospital trust policies, failing to recognise there was no danger at the flat, and failing to assess the life threatening nature of Ms Paterson's injuries.
Ms Paterson's boyfriend dialled 999 on the afternoon of 27 October and reported she was unconscious, breathing abnormally and her lips were blue.
As police had previously been called to the Hargrave Road address, and it was flagged as being on the High Risk Address Register, paramedics were told to wait for a police escort.
Ms Paterson, who had worked as a researcher at King's College Hospital, suffered a cardiac arrest at about 3.15pm, five minutes before police and an ambulance team arrived.
The delay caused her brain to be starved of oxygen, leaving her in need of specialist care in hospital for the rest of her life.
Her lawyer, John Davis, said it was not known why her property was on the high-risk register but that following the case it had been acknowledged it needed to be "radically overhauled".
'Admission of liability'
He said: "We endorse any review and improvement to this system which was clearly at the heart of the failings in this case."
Ms Paterson's mother, Eleanor Paterson, of Warkworth, Northumberland, welcomed the "admission of liability".
She said it was a "significant step towards ensuring Caren will continue to receive the care, treatment and specialist attention she will need for the rest of her life, but nothing will return our daughter to the way we knew her".
A statement from LAS said: "We carried out a detailed investigation into the circumstances of the incident and we have accepted liability for the shortcomings in the care that was provided on October 27, 2007.
"Dr Paterson is bringing a claim for compensation against the service and we hope that the legal representatives can now work together to find a resolution."