AN investigation was under way last night after Edinburgh's troubled new flagship hospital ran into another problem.

Malcolm Chisholm, the health minister, called for an urgent report after the (pounds) 184m Royal Infirmary at Little France suffered a power failure that left it without electricity for an hour.

The hospital's emergency generators were said to have failed to start, putting hundreds of lives at risk. Staff were forced to use battery back-up for critical areas like intensive care.

It was the latest in a series of problems that has plagued the PFI (private finance initiative) facility. Last month, about 40 members of staff had a ban on opening windows lifted after months of pressure from workers stifling in temperatures of more than 86F (30C).

Mr Chisholm said he was extremely concerned about the latest incident at the hospital, which became fully operational in May.

He said: ''This was a very serious failure. I want a report from NHS Lothian about this incident as a matter of urgency to see what lessons need to be learned.''

Lothian NHS Board is now demanding urgent talks with Consort Healthcare, the private company responsible for the hospital, which opened in January.

Brian Cavanagh, the board chairman, described the incident as ''intolerable''. He said: ''We have a duty of care to our patients and staff, and anything which breaches that is totally unacceptable . . . We are demanding an immediate meeting with Consort Healthcare, our PFI partners, who are responsible for the fabric and the maintenance of the hospital.

''We want absolute assurances that this problem with the generators will be sorted out once and for all.''

Consort Healthcare last night acknowledged the problem and said it would be investigating what had happened.

A spokesman said: ''We can confirm there was a power outage of approximately one hour. Back-up generators failed to cut in when mains power was lost. The reasons that the standby system failed to work as planned are being investigated. Consort takes this matter extremely seriously.''

A spokesman for ScottishPower stressed: ''At no point was there a loss of power from the ScottishPower grid to the hospital.

''There seems to have been a problem with the hospital emergency back-up generator which was resolved when the hospital reconnected itself to the grid.''

Shona Robison, SNP health spokesperson, said it was fortunate that no-one had died during the blackout and called for an immediate inquiry. She said it cast more doubts on PFI

projects.