Novichok agent
The helicopter was grounded while tests were carried out.
Officers are expected to be wearing protective clothing,
His mother’s body is currently 'property of the Crown'.
The search could last "months".
The container was found in victim's home.
It has also been revealed that the nerve agent ‘could remain active for 50 years’
The pair remain in a critical condition in hospital.
Substance poisoned ex-Russian spy Sergei Skripal.
The agent could be applied with an aerosol spray or transported in liquid form.
Government still blames Russia for attack.