Theresa May is facing mounting pressure to take decisive action against whoever was behind the nerve agent attack on an ex-Russian spy and his daughter, BBC reports.
Former national security advisor Lord Ricketts said "firm action" was needed once responsibility was confirmed.
Foreign affairs committee chairman Tom Tugendhat said evidence was mounting against Russia, which has denied involvement in the Salisbury attack.
Sergei and Yulia Skripal remain in a critical but stable condition.
The 66-year-old retired Russian military intelligence officer and his daughter, 33, were found slumped on a bench in Salisbury on 4 March.