Unions and NHS managers have presented MPs with a series of concerns over the private finance initiative, warning that the process may have become 'an end in itself '.

The Commons health committee is due to begin hearings for its inquiry into the role of the private sector in the NHS next week, when health secretary Alan Milburn will appear, but written evidence already submitted focuses primarily on PFI.

HSJ understands that the committee will hold an evidence session in North Durham, and possibly other places with major NHS PFI developments, as well as the more usual setting of the Commons committee rooms.

The hearings are likely to reignite the row between the unions and the government over the private sector's role.

But the NHS Confederation, which in its evidence criticises the polarised debate as 'confused and . . . burdened by ideology', also raises significant doubts about 'whether the promised benefits of the PFI process are available'.

It calls for a 'rigorous and comprehensive' assessment of the value for money of PFI schemes, warning that some of the transfer of risk factored into the cost 'has not been particularly valid'.

It also states that there is 'little evidence' that PFI produces innovative design. 'Indeed, reports from those involved in the process suggest. . . something of the opposite effect.'

A key criticism is the lack of any assessment of the impact of modernised working practices on hospital design. The process of agreeing a PFI deal has had more impetus and in some cases may have become 'an end in itself ', the confederation warns.

Policy director Nigel Edwards said there was no objection to the private sector in principle. But he added: 'It behoves all of us to take a more evidence-based approach.

And that means all of us - government as well as critics.'

Unison reiterated its opposition to PFI, calling on the MPs to support a moratorium and an independent review of all existing projects.

National officer Stephen Weeks said: 'We are concerned that the record of PFI hospitals that are up and running is mixed, to say the least. A significant number of the first wave have experienced service failures and design problems.'

The union's evidence highlights its concern at the creation of a 'two-tier workforce' through PFI.

But it also points to less frequently rehearsed concerns such as 'the phenomenon of refinancing' PFI schemes - similar to remortgaging a house - which it claims is a 'hidden subsidy to the private sector'.

Evidence from the MSF union claims 'there has been no real or sustained attempt through partnership to involve staff in service modernisation. . . our members are at a loss to understand why market mechanisms are being considered before this has taken place'.