The writer and broadcaster - who died yesterday aged 79 - told relatives she wanted her final words to be: "Tell David Cameron that if he screws up my beloved NHS I'll come back and bloody haunt him."
Rayner had devoted her life to caring for others - through her work as a nurse, an advice columnist and later as a campaigner for patients' rights.
She had not recovered from emergency intestinal surgery in May and knew her death was imminent over the weekend. She died in hospital near her home in Harrow, north-west London.
Her husband, Des Rayner, to whom she was married for 53 years, said: "I have lost my best friend and my soulmate. I am immensely proud of her."
Her death touched many with whom she had either worked or inspired.
Katherine Murphy, chief executive of the Patients Association - of which Rayner was president - said: "She was a figurehead and inspiration to us all.
"She cared so deeply that the voice of the patient should be heard and worked tirelessly to ensure that care issues were given prominence in all health matters. She was a wonderful person, an inspiration to us all and she will be missed so much by everyone."
Baroness Helena Kennedy said: "She was the best of company and could always be found in the middle of a laughing, adoring crowd.
"The key thing about Claire was that she was a campaigner to her toes - her mission was to improve the lot of others and she did it with great humility and common sense.
"Claire Rayner was a great force for good in British society. I feel bereft."
Fellow advice columnist Deidre Sanders, of The Sun, said Rayner would always stand by what she thought was right. She told ITV1's Daybreak: "She really doesn't mind what other people thought and she was very prepared to state her mind.
"She was such an amazing character, she was really larger than life."
Rayner, who wrote for the Sun, Sunday Mirror and Woman's Own, will be given a humanist funeral service for family and close friends only.
Rayner, also survived by children Amanda, Adam and Jay, and her four grandchildren, started her career in the National Health Service, working as a nurse.
Her husband, who was also her agent and manager, said: "Through her own approach to life she enabled people to talk about their problems in a way that was unique.
"Right up until her death she was being consulted by both politicians and the medical profession about the best way to provide the health services the nation deserved and nothing mattered to her more than that. Her death leaves a vacancy which will not be filled."
Rayner had an impoverished childhood before starting her working life. It was while on maternity leave to have her first child that she became a freelance journalist.
She became a household name as an agony aunt on problem pages in Britain's best-selling newspapers and also made numerous appearances on television and radio.
She was also a successful author, writing more than 90 books, both fiction and non-fiction.
In 1996 she was awarded the OBE for "services to women's issues and health issues".
She was involved with more than 50 charities, and was a member of the Prime Minister's Commission on Nursing and the last government's Royal Commission on the Care of the Elderly.
Her no-fuss attitude to health matters led her to being employed by the BBC to demonstrate how to put on a condom, and being one of the first people to advertise sanitary towels.
Her family have asked to be left to grieve in peace.
Her son, food critic Jay Rayner, told the BBC Radio 4 Today programme: "She had led an amazing life and I am very, very proud of her."
The British Humanist Association (BHA) - for which Rayner was vice-president and former president - expressed sadness at her death.
Chief executive Andrew Copson said: "Claire Rayner found meaning and inspiration in living and the enjoyment of life, in trying to fulfil her potential, and in the wonders of nature and the marvels of the cosmos."
Politicians also paid tribute. Liberal Democrat deputy leader Simon Hughes said: "Continuous work and campaigning to improve our National Health Service for all our patients will be the best sort of tribute our country can give her."
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