Health secretary Andy Burnham has written to Conservative Party leader David Cameron demanding information on the £21,000 donation from the wife of Care UK chairman John Nash to shadow health secretary Andrew Lansley.

The donation potentially raises “major questions about the independence of Conservative policy making,” the letter says.

The letter asks for a full breakdown of meetings and discussions with Care UK

It states: “At a time when public confidence in the political system has been shaken, we all have a responsibility to be as transparent as possible about the access given to stakeholders, particularly those who stand to benefit commercially from policy decisions.

“This is particularly important in the field of health policy, where there is still uncertainty about your precise plans for the NHS in government.”

Mr Burnham has asked Mr Cameron whether he thinks shadow cabinet members should accept private donations from companies that have a vested interest in their policy areas.

He also wants to know what safeguards Mr Cameron has put in place to “guard against any accusations or perceptions of undue influence in the policy making process”.

The letter asks for a full breakdown of meetings and discussions with Care UK and a “full and detailed commentary of all communications” between Care UK and the Conservatives.

Care UK runs hospitals, walk-in centres, GP practices and care homes available through the NHS.

The donation has raised eyebrows because of the emphasis the Tories have placed on opening up services to “any willing provider” and embracing the private and voluntary sectors.

But a Conservative spokesman said Labour had received millions of pounds from trade unions, which supported the party’s policy to treat the NHS as the “preferred provider”.

Prime minister Gordon Brown received £5,000 for his 2007 leadership campaign from Bupa chairman Lord Leitch, he added.

The spokesman said: “We have been completely transparent about this donation. It has been properly registered with the parliamentary register as well as with the Electoral Commission and is therefore fully within the rules.

“John Nash and his wife have a wide range of interests, of which Care UK is just one. Mr Lansley did not solicit this donation. Donations from private individuals in no way influence policy making decisions.”

The donation, made through Conservative Party headquarters, was to go towards running Mr Lansley’s office.