Many of the recent cases have involved cancer treatment
The policy of denying NHS services to patients who top up their care with private treatment is to be reviewed in England, the government says.
Health Secretary Alan Johnson has asked cancer tsar Professor Mike Richards to look at the issue.
Some patients have found themselves banned from NHS care after paying for cancer drugs not available on the NHS.
The government had argued that such a system of co-payments would create a two-tier service.
But it has now agreed to reconsider the issue and has given Professor Richards until October to report back.
THE CASE THAT CHANGED POLICY?
The Linda O'Boyle case is perhaps the one above all others that has been used by campaigners to press for change.
The 64-year-old, from Essex, was diagnosed with bowel cancer in 2006 and received NHS treatment, including chemotherapy, until September last year.
She then paid £11,000 for an eight-week course of a drug called Cetuximab, which is not available on the NHS, to prolong her life. But she was subsequently denied the basic package of NHS care she had been receiving.
She died in March and since then her husband and local MP have campaigned for the government to reconsider the rules.
Currently, anyone who pays for any form of private treatment - even drugs unavailable on the NHS - can be barred from the normal package of NHS care.
The rule applies across the UK and the Northern Ireland and Wales administrations said they would watch with interest the developments in England.
Scotland has already announced a review, although it is specifically on cancer drugs.
The issue has come to a head in recent months as a number of cancer patients have been banned from receiving NHS care after topping up their treatment.
Doctors and patients groups have opposed the stance taken and now the government has decided to act on the concerns.
Mr Johnson said guidance on the issue had existed for 20 years, but it was now time to get an "up-to-date view".
"This is a very complex issue so it needs to be reviewed. We want to be fair to everyone... while protecting the principles of the NHS."
Tory MP John Baron, who has campaigned on the issue following the death of his Billericay constituent Linda O'Boyle earlier this year, said: "It is a very welcome decision. The ban on co-payments is cruel."
Critics have pointed out that the rules have been inconsistently applied and in some areas of treatment, such as dentistry, not used at all.
Liberal Democrat health spokesman Norman Lamb said the announcement was "long overdue" and represented a "remarkable U-turn".
"If a patient chooses to pay for a drug that the NHS won't provide, then it is unjust to deny them treatment which is available to everyone else."
Shadow health secretary Andrew Lansley added it was right to review co-payments, but added: "We should also be looking at why these drugs are available in other countries and not here."
The decision by the government has also been welcomed by managers, doctors and patients.
Nigel Edwards, director of policy at the NHS Confederation, which represents health managers, said: "The impasse on top-ups was clearly unsustainable and threatened to undermine public confidence in the NHS."
Roger Goss, of Patient Concern, said the ban on co-payments was "ridiculous" and should be overturned as soon as possible.
And Christoph Lees, of the independent Doctors for Reform group, which has been threatening to take legal action over the ban, added: "This is a historic moment that points the way towards a modern NHS based around the needs of patients rather than bureaucratic rules."