Conservative MPs are being urged to oppose changes that deputy prime minister Nick Clegg wants to make to the government’s plans for NHS reforms.

In an email sent to all Conservative MPs and obtained by the BBC, Nick de Bois, who has previously said the fundamental principles of the overhaul would not be changed, has set out a series of “red lines” from which he says his fellow party members should not retreat.

He says critics of the bill have so far “made their voices the loudest”, and calls on the Conservatives to set out their own red lines - “the principles on which we will not budge”.

“I am determined that we reclaim the debate over the future of the National Health Service from those who seek to use the bill as a political tool,” he adds.

The email appears to contrast heavily with Mr Clegg’s plans.

Addressing charity representatives in London yesterday, Mr Clegg said there would be “no sudden, top-down opening up of all NHS services to any qualified provider”.

But Mr de Bois’s email says “government should do nothing that stands” in the way of any qualified provider, including private companies and charities, providing care.

Mr de Bois also says there should be a clear date - April 2013 - “when statutory responsibility must transfer from the top-down bureaucracy to GP consortia”.

But Mr Clegg said there should be “no arbitrary deadline” for that.

He also suggested NHS reforms could be delayed by weeks, if not months - as the Health and Social Care Bill could be set to go back to a committee of MPs for further scrutiny.

The bill passed the Commons committee stage at the end of March after two months of discussion before being “paused” as part of the government’s “listening exercise”.