Iain Duncan Smith has unveiled proposals to allow those needing medical treatment to shop around in the NHS and the private sector.

Setting out his "patients' passports" policy, the Conservative leader said he was determined to focus on quality of life issues in the run up to the next general election.

Treatment in the NHS would remain free of charge and those opting for private care would be "helped, not penalised" by a contribution to the cost of their operation.

While the full details of the policy have yet to be finalised, the party said it aimed to tackle the problem of existing "two tier" services.

Conservative officials hope that following a pledge to scrap university tuition fees, the new policy will also prove a vote winner with middle classes forced to choose between paying for private treatment or waiting for an NHS operation.

That party argues that at present choice of hospital treatment is only available to people who pay their taxes and then pay again for private healthcare.

Promising to make choice "universal", the passport policy would entitle patients to have their treatment paid for at any NHS hospital.

And "as capacity in the voluntary and private sector builds up" they will be able to take all or part of the cost of their NHS treatment to the voluntary or private hospital of their choice. However, the party is not yet stating explicitly how quickly the private sector will be brought into the passport scheme.

"We are consulting on what should be the right level of this entitlement," explained the party's policy document.

Whether patients take some or all of the standard tariff funding to voluntary or private hospitals is not yet clear.

Final decisions will be based on the cost, the level of available capacity, the predicted effect on NHS demand, the effect on the current private insurance market and the need to promote greater diversity in provision, said the party.

However, it is expected that it will become "a realistic option" for a much larger proportion of the population to have access to a wider range of healthcare providers than is now the case.

"Those who choose to have their health care provided within NHS hospitals will reap the benefit of shorter queues if more patients choose to have care elsewhere. Patients will, of course, be able to stay entirely in NHS hospitals if they choose: nobody will be compelled to go outside."

The Conservatives argued that people who pay more towards their own healthcare pay their taxes like everyone else and also save the NHS resources and cut waiting lists.

"They should be rewarded, not penalised. They deserve a fair deal too," said the party.

There is likely to be controversy, however, over the explicit aim to increase the share of health spending in the private sector.

"We want to see total spending on healthcare increase, but we want to see the proportion of spending that comes from other sources increase at a faster rate than that coming from the state.

"This will bring the UK more into line with the pattern of spending found in most of the European countries we have visited," explains the party.

Duncan Smith said the proposals "will mean fairer healthcare, with no-one left behind".

"Our proposals would also mean better healthcare for everyone, with choice driving innovation and excellence and more healthcare as we expand the capacity of the health system in Britain," the Tory leader pledged.

"Our proposals would mean nothing less than a revolution in healthcare."

Duncan Smith said that the proposals were based on the "founding ideals of the NHS" and would ensure that healthcare was free at the point of delivery.

"But, for the first time in its history, the NHS would become a truly national health service, embracing our belief that healthcare is first and foremost about the patient.

"Compared to that, everything else is surely secondary."