Patricia Hewitt, the health secretary, promised today to phase out the sweeteners enjoyed by private sector health corporations treating patients from the NHS waiting list.

In an article in the Guardian, she acknowledged the current contracts for independent treatment centres in England gave the private sector an unfair advantage in competition with NHS hospitals.

The first wave of treatment centres is building up to provide about 210,000 operations year, mainly involving cataract surgery and joint replacements.

Healthcare corporations from the US, Canada and South Africa were offered a premium price for the work - in some cases well over the standard NHS tariff - to encourage them to set up in Britain.

Under contracts agreed by Ms Hewitt's predecessor, John Reid, the corporations were also given guaranteed volumes of work, obliging primary care trusts to shift patients away from local NHS hospitals, disrupting the health service's normal income streams.

In the Guardian article, she pledged that this favoured treatment would stop. She denied that the private centres are allowed to operate at lower clinical standards and outside ethical recruitment policies, but conceded: "Other criticisms are justified ...

"We need to move towards a level playing field for all providers, where the amount paid for a treatment, the minimum standards and the information given to patients is the same for every provider treating NHS patients."

The British Medical Association complained this week that NHS hospitals were losing the opportunity to train junior doctors on straightforward operations that were shifting to the private centres. Ms Hewitt said: "It must be right for the independent sector to help train NHS staff." Four centres had already begun pilot schemes. The first wave of private centres have so far treated about 100,000 patients. Last month. Ms Hewitt announced a second wave, worth £2.5bn over five years.