Novichok agent
The testing is part of the investigation into the Novichok deaths of Dawn Sturgess and Charlie Rowley.
Dawn Sturgess, 44, died of the same Novichok toxin used on a former Russian spy four months ago.
The pair were hospitalized after being found unwell just a few miles from where an ex-double agent was attacked in March.
The chemical weapon was developed in secret in the Soviet Union in the 1980s.
