Outdoor education centres with impeccable safety records are seeing their insurance bills rocket because of fears that parents will sue.
Some local authorities, for example East Sussex, West Sussex and Camden, north London, are demanding that the centres have insurance worth pound;10 million instead of the customary pound;5m before they will agree to let their schools attend.
Surrey prefers centres to have pound;10m cover, and will ask for more depending on the level of risk the activity involves.
Marcus Bailie, head of inspection at the Adventure Activities Licensing Authority, a government-funded inspection body set up following the 1993 Lyme Bay canoeing tragedy when four teenagers drowned during a school trip, said: "It is outrageous that some LEAs are demanding that they have up to pound;10m in public liability insurance before they will use them.
"The centres are all going nuts because they are unable to get insurance at a rate they can afford."
Medina Valley Centre, on the Isle of Wight, had to find an extra pound;3,500 last year and pound;4,000 this year to cover its insurance premiums.
Peter Savory, head of Medina, which has had no claims made against it, said: "We have 2,000 children who use the centre each year, so that is an extra pound;2 each child has to pay."
A West Sussex spokeswoman said: "We ask for pound;10m cover because claims in recent years in other parts of the country have exceeded pound;5m in some cases. It is being realistic about the sums involved."
In an Office for Standards in Education report into outdoor education published last week, David Bell, the chief inspector, said that the cost of school trips was one of the reasons why most students did not take part in them.
Authority-owned centres are not immune to rising insurance bills. Tricia Zimmerman, director of Hengistbury Head centre, controlled by Bournemouth council, has seen her insurance premiums for sailing and canoeing rise from pound;3,000 to nearly pound;7,000 in two years. She said this has resulted in schools having to pay more. Hengistbury has never had a compensation claim made against it.
Bill Healey, deputy head at Claverham community college, East Sussex, said:
"The whole point of outdoor activities is the inherent risk. That's where the learning comes from.
"On an outdoors trip recently the supervising teacher spent pound;1,500 on hiring mountain bikes for the week, but later found the instructor did not have the qualification East Sussex demands so we could not use them."
According to the licence authority's statistics there were 57 deaths on school trips, 19 of which occurred during adventure activities, between 1985 and 2004.