Patricia Hewitt, the health secretary, gave the green light yesterday to plans for seven new hospitals to be built under the private finance initiative at a cost of £1.5bn.

Her decision to back the NHS's biggest ever tranche of investment will provide modern facilities for patients in Bristol, Peterborough, Middlesbrough, Wakefield, Tunbridge Wells, Chelmsford and Edmonton, north London.

But it added to anxieties among health service managers and union leaders that the NHS is locking itself into repaying huge sums in 30-year deals with the private sector for buildings and equipment that may not meet changing medical needs.

Ms Hewitt said the seven hospitals passed the Treasury's tests on affordability and value for money during a reappraisal of PFI schemes over the past few months. The new facilities would replace "inadequate and outdated hospitals across the country", including mixed-sex wards and dilapidated premises, parts of which dated back to the Crimean war.

They bring total investment in new NHS premises in England to £10.6bn since 1997, including 116 hospitals and 188 GP health centres. Andy Burnham, the health minister, defended the building of more hospitals at a time when the government is courting widespread unpopularity by closing NHS facilities. "In many cases, these are new hospitals for towns that have waited decades and are having to provide healthcare from clapped out facilities that are not fit for today's modern NHS," he said.

Sir Ian Carruthers, the former NHS acting chief executive, will present a report on hospital reconfiguration later this week. Mr Burnham said: "Where there's a case for changing services then let's take that forward because nobody should stand in the way of progress for whatever reason, because they are resistant to change."

The British Medical Association was concerned that PFI schemes were leaving NHS trusts with unaffordable debts. "The government seems intent on spending large sums of money in private sector deals, which have been shown on repeated occasions to offer poor value and can leave hospitals heavily in debt for decades. The future of these hospitals is being mortgaged while private companies make profits from the NHS," a spokeswoman said.

Karen Jennings, head of health for Unison, said: "What a shame the government has turned to PFI ... Already the extra cost of PFI for the first wave of 18 signed hospitals is almost £500m a year. The fallout for some hospitals has been devastating."

The schemes getting the go-ahead are:

· A £310m hospital with 830 beds for Bristol North and South Gloucester primary care trusts to replace Frenchay and Southmead hospitals.

· A £78m hospital with 312 beds for Tees and North East Yorkshire NHS Trust on the St Luke's site near Middlesbrough, replacing a 106-year-old building.

· A £282m hospital with 612 beds for Peterborough Hospitals NHS Trust on the Edith Cavell site.

· A £225m hospital with 512 beds for Maidstone and Tunbridge Wells NHS Trust, replacing two hospital buildings, parts of which date from the Crimean war.

· A £343m scheme for Mid Yorkshire NHS Hospitals Trust replacing outdated buildings at Pinderfields general hospital in Wakefield and Pontefract general infirmary.

· New facilities for Mid Essex Hospital Services NHS Trust with a £143m project in Chelmsford.

· A £111m scheme for North Middlesex University Hospital NHS Trust.

The Department of Health said the first of the new buildings were expected to open next year.