The Conservatives today demanded an inquiry into suggestions that a North-East hospital serving the constituencies of former Health Secretary Alan Milburn and Prime Minister Tony Blair had its star rating enhanced following ministerial pressure.

Shadow Health and Education Secretary Tim Yeo said he had written to Mr Blair on the claims about South Durham Trust, which served part of Mr Blair's Sedgefield constituency and Mr Milburn's Darlington constituency.

The Health Service Journal said it had seen an exchange of correspondence between an aide to Mr Milburn and Department of Health officials, from just before the 2002 ratings were to be announced, in which the aide queried why the trust had fallen from a three to a two star rating.

A day later, the ratings appeared to have been recalculated and South Durham's rating increased to three stars.

Mr Milburn declined to be interviewed for BBC Radio 4's Today Programme on the subject but gave it a statement in which he said: ''The allegation that I somehow secured higher ratings for particular hospitals is complete tosh.''

But Mr Yeo told the programme: ''We need a full inquiry into this. It does look like a terrible lack of integrity at the very heart of Government, in the Secretary of State's own private office, where cynicism seems to be displayed about the system of star ratings.

''If they are going to be manipulated on the basis of how important the MP which represents the hospital concerned is, that completely destroys any confidence the public could have in the whole system.''

The extra star had given the hospital access to an additional £1 million in funding, said Mr Yeo.