Health charities have demanded David Cameron be "bold" and establish a commission on the future of the NHS and social care in Britain, needed amid the challenge of an aging population.
In an open letter to David Cameron, 40 organisations warned the UK was facing "monumental demographic challenges" and that the current system was "underfunded".
The letter is signed by leading figures including Lynda Thomas, chief executive of Macmillan Cancer Support; David Sinclair, director of the International Longevity Centre; and Professor Martin Green, chief executive of Care England.
Other signatories include experts from the British Red Cross, the Stroke Association, Mencap, Marie Curie and the MS Society.
In the letter, the organisations say:
The letter comes after three former health ministers called for a cross-party commission to review the future of health and social care in England.
The organisations back that call, writing in the letter: "We are keen to work with you to make this commission a reality."
Simon Bottery, policy director at Independent Age, and one of the signatories, said it was "crucial" the UK was prepared for the fact the number of people aged 85 and over will double in the next 20 years to three million.
"We need to start talking now, honestly and openly, about what standards of health and care older people can expect now and in the future," he said.
A department of health spokesman said: "We know the NHS is facing challenges as our population ages, but we are absolutely committed to its future and are investing £10 billion more to fund the service's vision for the next five years."