Government legislation risks "diluting the Government's constitutional responsibilities with regard to the NHS", says the Lords Constitution Committee in its report on the Health and Social Care Bill.
The Health and Social Care Bill divides the Secretary of State's statutory duties for the NHS in England between the Secretary of State, a new NHS Commissioning Board and new clinical commissioning groups.
The Government stated that they do not intend to weaken the Secretary of State's accountability for the health service. But in its report, the committee says that it may be necessary to amend the Bill to put the matter "beyond legal doubt".
The committee also question whether the proposed changes to NHS political and legal accountability are necessary to achieve reform.
The Bill will be debated in the House of Lords on Tuesday 11 October.