Mrs Warren said: "We had the extension built so that my husband's mother could live in it. Shortly after she moved in, we noticed a nasty smell coming from the floor. We had tests done, and eventually we were told it was contaminated."
Mr Warren's 80-year-old mother was eventually taken ill and is now in a nursing home.
Although tests are continuing, it is not known how the chemical, which is recognised as a serious health hazard, got there. The land, part of the town's Cherry Tree estate, was previously owned by the Ministry of Defence. However, the MoD strongly deniesthat it ever used contaminants or dumped them on the site.
The Warrens' problem is not unique. According to the Department of Environment, there may be up to 100,000 contaminated sites in Britain, the majority in or near urban areas. The most common contaminants are lead, mercury and cadmium.
The Environmental Protection Act places a duty on the Waste Regulation Authority to inspect contaminated land and, if necessary, order the owner to pay for cleaning up the site. However, this is unlikely to happen in the Warrens' case.
Equally worrying is the effect that site contamination can have on a property's value. Normal conveyancing land searches do not reveal whether land is contaminated or not, although detailed records are kept of sites under which coal-mining took place.
The London-based ICC Site Search provides a contamination report on any site in the United Kingdom. It uses historical and ordnance survey maps to establish a site's former use.
Checks can also be carried out with relevant regulatory agencies, such as the National Rivers Authority and HM Inspectorate of Pollution.
Site Search's findings do not state whether the site is actually contaminated, only whether potential contaminants were used on it.
Once the report has been produced, a detailed inspection of the site may be necessary. Site Search promises to provide the initial report within 10 working days, for a cost of £259 plus VAT.
All this is now academic for Mrs Warren. In November, she and her husband were forced to move out of their Colchester home and into temporary accommodation, where they remain.
Mrs Warren said: "We have been left in limbo. They have been carrying out tests for most of the past year, but no-one has been able to tell us what caused it. The worse thing for us is not knowing what is going to happen.
"All we can tell is that the problem is confined to the extension for the moment. But if you can't live in one part of the house, then the whole house is affected anyway," she said.
o Site Search can be contacted at: 16-26 Banner Street, London EC1Y 8QE. Tel: 071-253 0699.