An inquest will open later into the death of a diabetic woman who had a heart attack after being forced to wait almost five hours for an ambulance.
Investigations have been carried out by both the London Ambulance Service and the NHS 111 helpline into how Lisa Day, 27, died on September 12 last year, her family said.
The type-one diabetic fell severely ill on September 7 and her case was referred to paramedics via the 111 service at 5.50pm, but an ambulance did not arrive until 10.30pm after a 999 call was made.
During the delay Ms Day's condition deteriorated and she suffered a cardiac arrest, eventually dying because her brain-stem was starved of oxygen.
Matthew Edwards, her brother-in-law who is representing the family at the inquest, said the time it took for Ms Day to receive medical care played a key part in her death.
He said: "Had even a first responder been in attendance with basic resuscitation equipment, even in half the time it took for them to arrive, her chances of survival would have increased hugely as they would have had a greater chance of keeping the brain stem alive by the delivery of oxygen."
Mr Edwards also said there were questions to be answered about the adequacy of the training of the paramedics who attended Ms Day and potential shortfalls in their equipment.
And he said there was a "huge oversight" by the NHS 111 service, as the operator who took the call did not ask whether Ms Day had any pre-existing conditions.
The inquest begins on Monday at St Pancras Coroner's Court.