Many people now beat cancer
There are now two million cancer survivors in the UK, research suggests.
A survivor is defined as someone who has either beaten cancer or a person who has been diagnosed but is living with the illness, thanks to treatment.
The government had put the figure at 1.2 million but research by Macmillan Cancer Support suggests two million.
But the charity said successful modern treatments left a "ticking time-bomb" for the NHS, with survivors facing psychological or physical problems.
The Department of Health says that its "survivorship initiative", launched in March, will improve services for former patients.
However, Macmillan says the number is now rising at 3.2% a year.
The figure of two million cancer survivors is based on data for England, multiplied to give a total for the UK based on population.
Macmillan Cancer Support plans to release specific figures for Wales, Scotland and Northern Ireland later this year.
Its chief executive, Ciaran Devane, said that the NHS only looked at the immediate side-effects of treatment.
One breast cancer survivor, from Berkshire, said the effects of the disease would stay with her for life.
She said: "I've had a mastectomy and chemotherapy, and I'm now going to be on medication for a few years.
"I've had bad reactions to some of the drugs such as panic attacks and burning sensations, and I've now developed hearing problems so I wear hearing aids."
A Macmillan survey revealed that many people, even after being successfully treated, still found it hard to carry out routine activities such as housework, or follow their chosen career.
However, the charity believes that many are not receiving enough support.
'No death sentence'
Mr Devane said: "The number of cancer survivors is growing every year and failure by Primary Care Trusts to put in place proper resources to care for these people is a ticking time-bomb.
"It is about time the NHS acknowledged that cancer is no longer necessarily a death sentence, and recognised its long-term impact on people's lives."
A spokesman for the Department of Health said: "We recognise that more needs to be done to support those people living with and beyond cancer and that is why the Cancer Reform Strategy announced the establishment of the National Cancer Survivorship Initiative.
"We welcome this new research from Macmillan Cancer Support who we are working very closely with to develop and implement this initiative."
The initiative will include work to improve the care of patients with continuing disease, as well as those who are "in remission", or free of cancer.