If schools do not take action to prevent computer problems at the beginning of the year 2000, they could fail to open for the new term, says the union, with predictions of disruption to heating systems, pay rolls and school administration.

The survey highlights the risk posed to schools which are connected to a central local authority security system, which could leave thousands of schools unprotected against burglaries if computers fail.

And it describes the problems that could affect computer software, threatening breakdowns and misunderstandings as 1999 changes to 2000.

Doug McAvoy has attacked the "complacency" of local authorities about the risk of computer failure

The survey, described as a "snapshot" of 16 local authorities in England and Wales, also found councils to be "complacent" about the potential dangers of computer failure to schools.

One authority had so far offered schools no support for the millennium bug, while five had still to check their central computer systems.

Only seven authorities had ensured that central and school computers would be millennium-bug resistant, prompting the General Secretary, Doug McAvoy to call for urgent action.

"It is extraordinary that so much complacence is being shown to the bug by education authorities. Few schools have the time or the staffing capacity to be able to do the necessary checks and changes themselves.

"The most alarming aspect of this survey is that many authorities are unaware of the potential scale of the problem and are taking no direct preventative measures to protect against the problems.

"The government must have a role here. Support from the special unit set up by the government should be available to schools and local authorities."