After passionate pleas by three members of the public, WNDC planners were forced to admit they had not realised the significance of the site and suggested there was a shortfall in archaeological expertise at local authorities.

The site between Gregory Street and Horseshoe Street currently houses a martial arts school and a taxi firm but was listed as a Scheduled Ancient Monument and a site of national historic interest following the discovery of Saxon remains.

Former conservation officer for Northamptonshire County Council, Martin Ellison, said: "This area needs much greater consideration and respect than it has been given in the planning report.

"I had expected a greater level of protest from English Heritage but unfortunately that has not been forthcoming. It is a disgrace that the factory could be demolished without consideration of further archaeological finds which might be discovered underneath."

Plans to demolish the building and turn it into 46 apartments and three commercial units had been approved in principle at an earlier meeting of the WNDC, but planning officer Adrian Arnold vowed to take another look at the history of the site and urged members of the committee to defer any decision until that had been done.

Archaeological digs at the factory have previously uncovered evidence of a medieval town and Saxon artefacts.

Councillor Penny Flavell (Con, St Crispin) said: "I am deeply concerned that it has taken the intervention of the public to come here to tell us of the significance of this site, and it is to their great credit that they have done so.

"Thank goodness they did, because this is a site of national importance."