Russia is feared to be rebuilding its spy network in Britain in the wake of the Salisbury nerve agent attack, MPs have been told.
Conservative Sir Roger Gale raised concerns as he pushed the Government to offer assurances that MI5 is very firmly on the case.
Home Secretary Sajid Javid declined to comment on intelligence matters but said Sir Roger is right to be concerned about the rise in hostile state activity.
A total of 23 Russian diplomats who Theresa May claimed were undeclared intelligence officers were expelled from the UK following the Salisbury attack.
International allies also followed suit, including the US.
Britain believes Russias GRU military intelligence agency was behind the Salisbury attack on former double agent Sergei Skripal and his daughter Yulia.
Both survived the poisoning in Salisbury but in July 2018 Dawn Sturgess died after coming into contact with Novichok which is believed to have been in a perfume bottle.
Scotland Yard and the Crown Prosecution Service believe there is sufficient evidence to charge two Russians – known by the aliases Alexander Petrov and Ruslan Boshirov – with offences including conspiracy to murder over the attack on the Skripals.
Speaking in the Commons, Sir Roger said: Following the attempted poisonings in Salisbury, the Prime Minister took robust action to secure the dismissal from the United Kingdom and other European countries of Russian spies posing as diplomats.
There is some reason to suppose that that network is being rebuilt.