School budgets are facing increasing pressure from a surge in mobile phone ownership, according to a teaching union spokesman.

John McNally, of the National Association of Head Teachers, says school telephone bills are set to soar because of a growth in the number of parents giving mobile phone contact numbers.

He says schools will have to make extra provision in their budgets for increasing phone bill costs, and could have to spend money earmarked for other resources.

Daytime calls made to mobile phones can cost up to about six times as much as calls made to British Telecom landline numbers.

Mr McNally, who is head teacher of a Birmingham primary school, said that around 20% of parents of pupils at his school had given staff mobile telephone contact numbers. This included a significant number who had done so since Christmas.

Some parents no longer used landlines, and relied solely on mobile phones, he said.

"We have to phone home in cases of illness, absence, or even if a child has left their swimming things behind.

"The cost of phoning more mobile phones is quite significant, when you have to count all the pennies in the pound.

"We don't really know what the extra cost will be yet, but schools will have to take it into account, and could have to use money needed for something else."