Foreign Secretary Boris Johnson has threatened to put a block on England travelling to this summer's World Cup following the alleged poisoning of a former spy on British soil.

Ex-double agent Sergei Skripal and daughter Yulia are currently critically ill in hospital after being found unconscious in Salisbury on Sunday.

Speaking in the House of Commons, Johnson suggested that England will boycott Russia 2018 if Moscow was shown to be behind the incident, with the pair being exposed to an "unknown substance".

"If things turn out to be as many members on both sides of the house suspect that they are, I think we will have to have a serious conversation about our engagement with Russia," he said.

"For my own part, thinking ahead to the World Cup this summer, I think it will be very difficult to imagine that UK representation at that event could go ahead in the normal way. We would certainly have to consider that."

England's World Cup campaign is due to get up and running with a match against Tunisia in 104 days.