Twenty-seven unexploded bombs were blown up under controlled conditions at a former air base near the site for 700 proposed new houses.

The Second World War explosives were found by workmen digging a security trench for a car distribution firm which stores vehicles at the former base at Upper Heyford.

Keith Watson, managing director of the consortium which manages the base site on behalf of the Ministry of Defence, said: "We called out the Army Bomb Disposal unit and also Thames Valley Police when 27 small unexploded RAF Second World War practice bombs were discovered in one long trench. Some of them were badly corroded."

The North Oxfordshire Consortium includes three house-building companies which want to build more than 700 homes at the former base. The consortium has long maintained that the risk of explosive contamination was small, as the site had been swept for explosives.

Mr Ian Lough-Scott, secretary of the Cherwell Valley Parishes, an association of residents of parishes adjoining the former base, said: "Clearly this is worrying. We were always assured that the site had been swept. Now we wonder how many more might be there."