Parliament will not be able to properly scrutinise one of Gordon Brown's new health ministers, the Liberal Democrats claim.
Lord Darzi has been put in charge of a fundamental review of the NHS, dubbed NHS Next Stage, and was given a peerage when he joined the Prime Minister's "government of all the talents".
But Liberal Democrat Norman Lamb said the surgeon - who will continue to practise in the NHS - will hardly ever be available to answer questions.
The North Norfolk MP said: "Given that he is embarking on a fairly fundamental review of the way in which the health service operates ... how on earth is Parliament supposed to hold him to account?
"Isn't this precisely the sort of arrangement the new Prime Minister indicated he was against, where effectively Parliament is being sidelined?"
But Health Secretary Alan Johnson said: "It's really in everyone's benefit to have someone of the reputation, the skill of Lord Darzi, who will continue to be a leading clinician in the NHS.
"I think it's innovative that we have not only got a clinician of his standing to lead this review, we have also got him as a minister to ensure that ... it's actually got someone in government to carry this through.
"I think that's of more interest to the public than who is answering questions in the Lords."