The letter went to St John's main funders - the Ministry of Health and the Accident Compensation Corporation - last year ahead of a report by the Health and Disability Commissioner's office which made "adverse comment" on a doctor and St John, and found a St John paramedic in breach of the code of patients' rights over his care of Marlene Dormer, who died in his single-crewed ambulance in 2013.
Mrs Dormer's daughter, Sherrill Clayton-Reed, told the Weekend Herald her mother would have survived if she was taken to the medical centre when the fully-crewed ambulance first attended, or if during the second callout hours later an ambulance volunteer or even a firefighter had joined the then-solo paramedic.
Associate Health Minister Peter Dunne said the Government was aware of the single-crewing issue and it was under discussion with St John.
He didn't answer whether St John would be funded to a level that permitted an end to its part-charge.
Mr Bradley said St John might have to consider increasing patient fees to make up any budget shortfall.
It currently levies a part-charge of $88 for an emergency ambulance to carry a patient not covered by ACC.
In the letter he says the current ambulance funding model, which relies too heavily on charity and on St John finding increasing levels of commercial income, is "not fit for purpose".