HALF the classrooms at Francis Coombe School in Horseshoe Lane, Watford, were left blackened and sooty after a computer caught fire on Saturday night.

Fire crews from Garston, Watford and Abbots Langley were called to the school just after midnight to find the ground floor thick with smoke.

Four firefighters wearing breathing apparatus traced the source of the fire to a computer in a claasroom which is thought to have overheated and burst into flames.

Sub-officer John Magill from Garston Fire Station said: "There was extensive smoke and fire damage to the whole classroom and 50 per cent of the other classrooms had varying degrees of smoke damage."

He explained the extent of the damage was caused by the school's air-conditioning system wafting smoke around the building.

He said: "Most of the classrooms should be OK after a quick clean but some will need a lot more work."