The Arson Prevention Bureau, set up by the Home Office and supported by the insurance industry, says that last year the cost of 1,400 school fires was £43m.

The Bureau's Tony Baker tells BBC News that 85% of all school fires are arson

In an attempt to reduce the threat, which costs the equivalent of 10,000 school places a year, the Bureau is publishing advice on how schools can protect their buildings - particularly during the peak arson period of the summer holidays.

The campaign was launched at St Brigid's School, Knowsley, Merseyside, with a seminar offering advice on preventing arson.

It was attended by the Home Office Minister, George Howarth, and representatives of local education authorities, schools and the emergency services.

Headteacher Gill Price says that school fires are a "devastating" experience

Mr Howarth said the venue was particularly appropriate as St Brigid's had suffered three fires, the last of which had totally destroyed the school.

School arson, he said, was a "particularly pernicious crime" which he hoped would be reduced by the awareness-raising campaign.

St Brigid's headteacher, Gill Price, said that the impact of school fires was "devastating, with so much work and effort lost".

Gill Price tells BBC News: "It's not a fortress"

The re-built school now has a number of security features which have protected the buildings from further attempts at arson.

Merseyside Fire Brigade's Mike Harris said giving schools extra security was expensive, but in the longer term was "worth the investment" when compared to the cost of replacing schools.

Merseyside is one of the areas in which arson attacks on schools are most frequent, along with Greater Manchester, London and the West Midlands.

In contrast, counties in the south west, such as Devon and Cornwall, have few problems with school arson.

The advice from the Arson Prevention Bureau, which will be sent to all schools, says that premises should be more carefully secured, with fences, alarms and security cameras. Schools should also take particular care of rooms which might hold combustible material.

In its research into school fire-raisers, the Bureau found that the typical arsonist was a boy aged between 10 and 16 and was often a pupil or former pupil of the attacked school.

Grudges against school

Among the claimed motivations of arsonists are grudges against schools or teachers, attempts to put off exams or vandalism that gets out of hand.

The most common times for starting fires was between 6pm and 10pm, particularly for primary schools.

Another important warning sign for schools, the Bureau says, is that serious arson attacks are often preceded by break-ins, vandalism or minor fires.

The chief executive of the Arson Prevention Bureau, Tony Baker, said: "The current level of arson attacks is unacceptable.

"Arson not only causes widespread and expensive damage but can severely disrupt pupils' education, impacting on morale and performance of the school for many years."