Ian McKenna, founder of F&TRC, said he had become increasingly aware of issues where families have been left facing huge debts, simply because GP surgeries have taken weeks - even months - to return forms to insurers.
He told FTAdviser it could even be classed as "gross negligence" because patients and their families are left facing enormous financial stress at a critical time.
McKenna said: "Can there be any worse situation than having a really serious illness, for which you are insured via either a critical illness or income protection claim, and your insurer cannot pay out because the doctor can't be bothered to return the forms?
"We are seeing multiple cases people are experiencing real and unnecessary suffering because of this medical negligence."
He claimed: "I know of someone whose cancer had been in remission for so long, that their insurers were willing to look at new proposals for new cover.
"But the doctor took so long to submit the information - we are talking about several months here, that the cancer actually returned and the person is now uninsurable."
While admitting that some doctors are "great", he said there were too many others who see insurance as unnecessary admin and have a "negative attitude".
Responding to requests from insurers is not healthcare, and is not NHS work.Dr Clare Bannon
McKenna (pictured, left) also said some GPs have been asking brokers' clients for up to £500 per insurance claim forms.
But there is not always time in the GP's day to process forms.
Richard Freeman, founder of Medi2Data, told FTAdviser: "I pay all due respect to the protection market but they need to think about the impact of their instructions on a GP surgery.
"From Medi2Data's research, we found there were approximately 3mn policies sold every year. Of the inbound applications, 10 per cent require GP information.
"But on top of that, GPs need to deal with the Department for Work and Pensions, the Ministry of Defence and solicitors. All these instructions come into a GP surgery."
Dr Clare Bannon, the British Medical Association's England GP committee deputy chairperson, said: "The public will be only too aware of how overstretched practices are, battling daily to meet the needs of patients amid mounting demand and with falling numbers of staff.
"At times of such severe pressure, practices are understandably prioritising the immediate healthcare needs of patients.
"While important for individuals, responding to requests from insurers is not healthcare and is not NHS work, meaning that it must be lower priority than looking after sick patients."