Schools were warned of the risks of e.coli in farm visits two years ago, according to the Department for Education.

It says any schools planning similar field trips or farm visits should re-assess the potential dangers.

This follows the award in the High Court of £200,000 as an initial compensation payment to the family of Tom Dowling, a six-year-old who suffered severe brain damage after contracting e.coli on a farm visit.

The boy, who became infected during a trip to Bowman's Farm in Hertfordshire in 1997 (before the publication of the education department's guidelines), now cannot move his arms or legs and can only communicate through blinking.

The boy's family claimed that the local authority should have checked the farm for e.coli - and it is expected that the final payment of compensation will be several million pounds.

The education department says that it has written to all local education authorities about the risk of e.coli in farm visits and has specified the risk in its guidelines on safety precautions for out-of-school activities.

'Wary'

But the ruling is likely to make head teachers even more cautious about taking children out of school, said Chris Purser, spokesman for the National Association of Head Teachers (NAHT).

"It's likely that that head teachers will be even more wary about school trips. It could be another blow to organised trips."

Mr Purser says that concerns over compensation claims and the cost of litigation has already made schools sensitive to the risks of trips.

Schools at present have to prepare a safety policy for out of school activities, which must include a risk-assessment of trips.

And the NAHT advises its members to get permission from parents wherever there are potential risks.

Parents also have the right to withdraw children from trips and, if the trip is part of the curriculum, can require the school to offer the same lessons within the school.

If pupils have to use private transport to get to an out-of-school acitivity (such as a lift in a car from a teacher or another parent), parents can also refuse to allow their child to participate.

'Very rare incident'

But the education spokesman for the Local Government Association, Graham Lane, expressed concern that fears about risks would reduce the number of school trips.

"We have to be careful that we don't end up with schools unable or unwilling to go anywhere because of potential risks."

The ruling has made the farm owners and Barnet council share liability for the compensation - with the council taking responsibility as the employer of staff at the school.

While the local authority declined to comment on the ruling, its insurance company, Zurich Municipal, said that this was a "very rare and very unfortunate incident, which had now been amicably settled".

Zurich Municipal, which insures about 80% of local education authorities, says that a majority of state schools are covered by a collective local authority insurance policy which covers such claims.

As a result of the case, company spokesman David Forster said he expected that local authorities and schools would take another look at their safety procedures to see how such cases might be preventable in the future.