Proposed Liberal Democrat amendments to the government’s troubled health reforms have been dismiseed by Labour as “cosmetic” changes designed to help Nick Clegg face down unrest within his party.

In a highly unusual move, the deputy prime minister and senior Lib Dem peer Baroness Williams wrote to the party’s parliamentarians yesterday backing changes to the legislation to limit competition in the health service.

Mr Burnham claimed the move was either “pre-agreed coalition choreography” or a sign of a government “in complete disarray”.

Health secretary Andrew Lansley, forced to cancel a planned speech after being summoned to the Commons to answer Mr Burnham’s question, told MPs the letter from Mr Clegg and Lady Williams simply explained “some of the amendments which we have been working together on”.

Addressing a raucous Commons, Mr Lansley said it was the “most scrutinised public bill in living memory” and ministers had been “open to any further changes that would improve or clarify” the legislation.

Mr Lansley said the letter from Mr Clegg and Lady Williams explained “their support for the bill with those changes and some further amendments they wished to see”.

“They said, for example, how we must rule out beyond doubt any threat of a US-style market in the NHS.

“I wholeheartedly agree. The bill is about quality, not competition on price.

“It will not permit any NHS organisation to be taken over by the private sector, it will put patients’ interests first.

“The bill does not permit any extension of charging, care will be free based on need.”

Where competition was in the best interest of patients, based on quality not price, it could “play an important role in driving up standards throughout the NHS”.

But “we will not see a market free-for-all or a US-style insurance system in this country”.

Motioning to Lib Dem MPs, Mr Lansley said: “We - and I do mean all of us on these benches - we are using the debates in the Lords further to reassure all those who care about the NHS.”

Mr Burnham said: “On Friday the prime minister promised no more amendments.

“Yesterday lunchtime the minister of state [Simon Burns] said the whole of government backed the bill as it stood. Hours later the deputy prime minister called for changes to a flagship bill that he has supported all the way.

“The government appears in complete disarray - or maybe it was pre-agreed coalition choreography to save face for the deputy prime minister.

“Either way, this House is entitled to ask: What’s going on?

“The NHS matters too much for it to be carved up in the unelected House in cosy coalition deals.”

He demanded to know when Mr Lansley was made aware of the letter, whether he had seen it in advance, if he had been overruled by Mr Clegg.

Mr Burnham asked: “Who is in charge of health policy, is anyone in charge?”

The shadow health secretary said Lib Dems had “played up” the changes but Mr Lansley’s department had dismissed them as “minor”.

Labour’s view was that the changes “did not affect the substance of the bill” but were “cosmetic changes designed to make the deputy prime minister look good in advance of his spring conference”.

Mr Burnham said the Lib Dem amendments were “empty gestures designed to save face” and that “in their heart of hearts …[they] hate this bill but haven’t had the guts to stand up to the prime minister and say so”.

Mr Burnham said the two ruling parties were “putting their political pride before the best interests of the NHS”.

The health secretary countered: “My right honourable friend [Mr Clegg] together with Baroness Shirley Williams was explaining to their Liberal Democrat colleagues the amendments which we have been working together on in order to make sure there is further reassurance, that is literally true.”