Britain's ambassador to the Organization for the Prohibition of Chemical Weapons (OPCW) said on Thursday that a briefing arranged by Russia and Syria on the OPCW's premises was a stunt.
Russia and Syria say they have brought several Syrians from Douma, where the OPCW is investigating possible use of chemical weapons in an April 7 attacks, as proof that no chemical attack took place.
Ambassador Peter Wilson said any witnesses should be interviewed by OPCW investigators instead, adding that Britain and its allies would not attend.
"The OPCW is not a theatre" he said in a statement.