The UK would respond “robustly” to any evidence of Russian involvement in the collapse of former spy Sergei Skripal, Boris Johnson has said.

Mr Skripal, 66, and his daughter Yulia, in her 30s, are critically ill in hospital after being found unconscious in Salisbury, Wiltshire.

The foreign secretary said he was not pointing fingers at this stage, but described Russia as “a malign and disruptive force”. Russia has denied any involvement.

Counter Terrorism Police have taken over the investigation from Wiltshire Police. But in a statement, the unit said the inquiry had not been declared a terrorist incident and there was no risk to the wider public.

Mr Skripal – a former Russian agent convicted of spying for Britain – and his daughter were found slumped on a bench outside a shopping centre on Sunday afternoon.

Earlier they were seen walking through an alley leading from a Zizzi restaurant, which has now been “secured” by police. The Bishop’s Mill pub has also been cordoned off “as a precaution”.

Scientists at Porton Down – the UK’s secret weapons research facility in Wiltshire – are studying the “unknown substance” that is thought to have made the pair ill.

Mr Johnson told MPs: “Honourable members will note the echoes of the death of Alexander Litvinenko in 2006. “And while it would be wrong to prejudge the investigation, I can reassure the House that should evidence emerge that implies state responsibility, then Her Majesty’s Government will respond appropriately and robustly… “I say to governments around the world that no attempt to take innocent life on UK soil will go unsanctioned or unpunished.”

Mr Johnson said that if it emerged Russia was linked to the incident in Salisbury “it would be very difficult to imagine” that UK representation at this summer’s football World Cup could go ahead in the “normal way”. The Football Association said it believed this was in reference to a UK government presence in Russia during the tournament and not in relation to the England football team. He said the UK was “in the lead across the world” in trying to counteract a “host of malign activity” by Russia.

But in a statement quoted by the RIA Novosti news agency, the Russian embassy in London said: “Media reporting could give rise to the impression that this is a planned action by the Russian security services, which in no way corresponds to the truth.”

Russia has insisted it has “no information” on what could have led to the incident, but says it is open to co-operate in the police investigation if requested.

Police are currently examining CCTV footage, filmed by a Salisbury gym, showing an unidentified man and woman walking near the location where Mr Skripal and his daughter were found.

Wiltshire Police has said two officers caught up in the suspected contamination have been treated in hospital for minor symptoms, before they were given the all clear. It is understood their symptoms included itchy eyes and wheezing. A third member of the emergency services remains in hospital.

Col Skripal, a retired Russian military intelligence officer, was jailed for 13 years by Russia in 2006. He was convicted of passing the identities of Russian intelligence agents working undercover in Europe to the UK’s Secret Intelligence Service, MI6.

In July 2010, he was one of four prisoners released by Moscow in exchange for 10 Russian spies arrested by the FBI as part of a swap. He was later flown to the UK.

The possibility of an unexplained substance being involved has drawn comparisons with the 2006 poisoning of Alexander Litvinenko. The Russian dissident and former intelligence officer died in London after drinking tea laced with a radioactive substance.

A public inquiry concluded that his killing had probably been carried out with the approval of the Russian President, Vladimir Putin. Mr Litvinenko’s widow, Marina Litvinenko, said the latest incident felt like “deja vu” – and called for those receiving political asylum to be “completely safe”.