Up to 15% of NHS operations may be contracted out to private firms, the health secretary John Reid said yesterday in a significant ratcheting up of the government's aspirations for privatisation of the health service.

Mr Reid was announcing the signing of a contract with Netcare, a South African healthcare corporation, to perform 41,600 cataract operations over the next five years in mobile surgery units that will travel around hospitals across many parts of England. This treatment will be provided free to patients on the NHS waiting list, starting next month.

The deal is part of a £2bn programme to crack the NHS waiting list problem by importing capacity from abroad. Six other companies from South Africa, Canada and the US have been declared preferred bidders to build and run operating theatres attached to NHS hospitals, but their contracts are not yet finalised.

The programme was outlined in September, but Mr Reid went further yesterday when he was asked on BBC Radio 4's Today programme whether it could lead to the NHS becoming a commissioning body contracting out all its work to the private sector.

He said: "For the foreseeable future, certainly in my lifetime, the NHS will not only be the main provider of health care in terms of commissioning, but will overwhelmingly be the direct provider. For the indefinite future, I envisage we would be bringing in perhaps 5% of the operations. It could go up to 10%, maybe (reaching a) maximum over our lifetime about 15%." It was the first time a minister let slip in public that the private sector could be given such a large foothold in a health service that for more than 50 years has been extolled as the jewel of Labour's approach to public sector provision.

A Department of Health spokeswoman said the 15% maximum was "not set in stone." Mr Reid was not suggesting contracting out 15% of the NHS budget, currently £60bn, rising to £80bn by 2008, but may have had in mind the proportion of elective (non-emergency) operations.

The NHS did 4.26m elective operations in England last year and 15% of that would be 639,000 that could be performed in the private sector. As the NHS expands, however, that number could increase.

Unison, the public service union, said: "The government is creating an unhealthy reliance on the private sector which will undermine the NHS."

Liberal Democrat health spokesman Paul Burstow said: "Setting up treatment centres that cream off the easy and profitable operations will leave the NHS to pick up the bill for complex high-cost operations.

Paul Miller, chairman of the British Medical Association's consultants' committee, said: "We welcome the extra capacity, but we want to be sure that the training of future consultant surgeons is protected if thousands of operations are performed in private units."

Mobile medics

· From next month NHS patients will be able to have cataract surgery in mobile operating theatres that will park for a day or two at hospitals throughout England.

· There will be two mobile units staffed by South African doctors and nurses. No NHS staff will be poached.

· The units will be run by Netcare, a private company that has 45 hospitals and 53 primary care centres in South Africa, treating more than 3 million patients a year.

· The units will visit hospitals in Devon and Cornwall, Dorset and Somerset, Hampshire and Isle of Wight, Surrey and Sussex, Kent and Medway, Thames Valley, Cheshire and Merseyside, Cumbria and Lancashire and Northumberland and Tyne and Wear strategic health authorities.

· The five-year contract is worth more than £40m. The average price of a cataract removal will be £840, compared with an equivalent NHS price of £940.

· Cataract surgery does not require an overnight stay in hospital, so patients should not be inconvenienced by the unconventional operating theatres. If they miss an appointment, however, they could face a lengthy delay before the mobile clinic returns to the area.

· Evan Harris, the Liberal Democrat MP whose Oxford constituents will be affected by the transfer of work away from the Oxford Eye hospital, has criticised the deal. He said the NHS price had been artificially raised to make the Netcare bid look more attractive, and warned of hospitals losing work to a company that had yet to prove its clinical competence in this country. The National Audit Office is to investigate the deal at his request.

· Richard Friedland, the chief operating officer of Netcare, said he hoped the contract would be extended beyond five years. "We are looking for a longer term partnership," he said.