Sergei Skripal
The pair were arrested and expelled.
The decontamination is part of a scheduled programme to make Salisbury and Amesbury safer.
Theresa May announces that an arrest warrant has been issued for two Russian men for the attempted murder of Yulia and Sergei Skripal, with the nerve agent Novichok in Salisbury. British authorities say the two men are officers from the Russian military intelligence service known as the GRU.
Detectives trained to memorise faces are trawling CCTV footage.
Use of a chemical weapon in violation of international law, says State Department.
Officers think several Russians were involved in the attempted murders.
The five things you need to know about politics today
Substance poisoned ex-Russian spy Sergei Skripal.
Officers have scoured more than 4,000 hours of CCTV footage.
'There was a real concern as to how big could this get.'