The investigation into the possible poisoning of the Russian spy Sergei Skripal gained new momentum on Tuesday, as Scotland Yard announced its counter-terrorism police would take charge, and the foreign secretary, Boris Johnson, promised a “robust” response if the Kremlin’s role in the case was proved.

Skripal was found slumped unconscious on a bench in Salisbury on Sunday afternoon. The woman discovered next to him has been identified as Skripal’s 33-year-old daughter, Yulia. Both remain critically ill and in intensive care after exposure to an “unknown substance”.

The Metropolitan police said that due to the “unusual circumstances” its counter-terrorism unit would now be heading the investigation. The police presence in Salisbury was stepped up on Tuesday, as specialist officers appeared around a police cordon.

Read more: The Guardian (UK)