First Minister of Scotland Alex Salmond has told Good Morning Britain that he believes Prime Minister David Cameron asked US President Barack Obama to make an "intervention" on Scottish independence.
Speaking to GMB's Susanna Reid, Alex Salmond said that although he felt the intervention was a "surprise", he felt that David Cameron had asked "every world leader he could possibly imagine to make interventions about Scottish independence."
More top news
The threat level has been raised to critical by MI5's Counter-Terrorism Analysis Centre.
Prime Minister Theresa May announced the decision from Downing Street.
A man, apparently armed with a small axe and a large stick, was detained close to the event and police cleared the area as a precaution.