Dawn Sturgess, 44, and 45-year-old Charlie Rowley remain critically ill after they were exposed to the toxic substance in Amesbury in Wiltshire.

The town is just eight miles from Salisbury, where former spy Sergei Skripal and his daughter Yulia were poisoned with Novichok in March.

The latest incident has further deepened tensions between the two countries, with British Home Secretary Sajid Javid calling on Russia to explain "exactly what has gone on".

Britain's Security Minister Ben Wallace claimed the "working assumption" is that the pair were exposed to the substance, a Soviet-era military-grade nerve agent, as a result of the attack in Salisbury "or something else".

The Kremlin has hit back by insisting Russia had nothing to do with the poisoning, while the Russian Embassy in The Netherlands tweeted it would be "dumb" for the country to carry out such an attack during the World Cup.

"How dumb they think Russia is to use 'again' so-called 'Novichok' in the middle of the FIFA World Cup and after the special session of the CSP (convened by the way by Britain) that gave the Organisation for the Prohibition of Chemical Weapons attribution functions, read the tweet. 

"The show must go on?"

Sergei Zheleznyak, a Russian Member of Parliament on the Duma's Foreign Affairs Committee, went a step further, accusing Britain of choosing Sturgess and Rowley to "create this strange and unpleasant incident".

"Their friend called the police and an ambulance and when the story became known to British officials and the secret services, they decided to use it as another case in this wild story about Russian spies, toxic substances and anti-Russian hysteria," he told Russia24.

"It's not a planned incident but an opportunity which British officials are trying to use."

The attack in Salisbury prompted the British Government to confirm the Royal Family and Cabinet Ministers would boycott the World Cup in Russia.

It also led to suggestions from some that the English team should not travel, although these were quickly dismissed by the Football Association.

The political tension between the two nations is also thought to be behind the small number of England fans in Russia, considered to be their smallest following at a World Cup in recent memory.

Russia 2018 chief executive Alexey Sorokin has urged England supporters to travel to attend the tournament, stressing that all fans are welcome in the country.

England play Sweden in the quarter-finals at the Samara Arena tomorrow.