A headteacher and contractors building a new school were evacuated yesterday while bomb disposal experts blew up war-time practice bombs and flares.

An RAF bomb disposal team carried out five controlled explosions at disused chemical waste pits at Chilton Primary School near Harwell International Business Centre.

The bombs were part of a large cache of munitions - including .303 bullets and 20mm cannon shells - uncovered by contractors cleaning up a 20-acre waste dump next to the primary school.

The dump was used for laboratory waste from Harwell Laboratory until the 1970s.

The waste pits contain a toxic cocktail of materials, including some low-level radioactive waste, much of which has already been removed.

During the Second World War, the dump was used as a bomb store for the former RAF Harwell airfield.

On Wednesday contractors uncovered 5,000 .303 rounds, a quantity of cannon shells, a dozen practice bombs and flares.

The Atomic Energy Authority owns the pits.

Spokesman Nick Hance said: "The ammunition and shells were taken away yesterday for disposal by ordnance staff from RAF Wittering.

"The practice bombs with their thin casing were felt to be less stable than the ammunition and cannon shells, and the decision was taken to deal with them with a series of controlled explosions on the site."

Contractors who had started site works on a new school were evacuated along with headteacher Christine Dunsdon, who was on the premises.

An area extending over a 250m radius including the school was cordoned off, and UKAEA staff visited residents in nearby Severn Road and the Horse and Jockey Guest House telling them to stay indoors during the explosions.

Windows were left open to reduce the risk of blast damage.