The National Union of Teachers has voted to fight the government's plans to open 200 city academies.

The union is to send teams of officials to oppose efforts to establish academies in place of underperforming comprehensives.

Delegates at its annual conference in Gateshead backed calls to initiate "action strategies" at any school that is identified as a candidate for conversion into an academy.

Tony Blair has pledged to open 200 academies by 2010 in a programme which will cost £5bn.

Each has a private sponsor who is given control of the governing body and influence over the curriculum in return for a contribution of £2m towards the construction costs.