FOREIGN Secretary Boris Johnson has vowed that any attempt to kill on British soil "will not go unsanctioned or unpunished" as police investigate the suspected poisoning of a former Russian spy.

Speaking in the House of Commons this morning, Mr Johnson told MPs that, although it is "too early to speculate" the cause of the unexplained collapse of Sergei Skripal, 66, at the Maltings in Salisbury on Sunday, but said the government would take whatever measures it deemed necessary.

Mr Johnson was summoned to the Commons after Tom Tugenshat, the chairman of the Foreign Affairs Committee, secured an emergency debate on Russia's 'soft war' against the West.

In his speech, Mr Johnson said: “There is much speculation about the disturbing incident in Salisbury.

"Police together with partner agencies are now investigating." 

He added that the incident has "echoes" of the death of Alexander Litvinenko, who was poisoned with the radioactive substance polonium-210 at a London hotel in 2006.

"While it would be wrong to prejudge the investigation I can reassure the house that, if evidence emerges that implies that state responsibility, then Her Majesty’s Government will respond appropriately and robustly," Mr Johnson said. 

"It is too early to speculate as to the precise nature of the crime or attempted crime that has taken place in Salisbury but I know members will have their suspicions and I will say if those suspicions are proved to be well founded then this government will take whatever measures we deem necessary to protect the lives of the people in this country, our values and our freedoms."

He added: "Though I am not now pointing fingers I say to governments around the world that no attempt to take innocent life on UK soil will go either unsanctioned or unpunished.

"It may be that this country will continue to pay a price for our continued principal in standing up to Russia but I hope this government will have the support of both sides of this house in continuing to do so."

Mr Johnson also thanked the “professionalism of response” of the emergency services.