Brett Lovegrove

Superintendent Brett Lovegrove, head of counter-terrorism for the City of London Police, said Edinburgh was an "extremely attractive proposition" for terrorists.

Mr Lovegrove told the anti-terrorism conference in Edinburgh, which aimed to equip workers to spot possible threats, "It isn't a case of 'if' there will be an attack on Edinburgh but 'when'.

"In particular, the festival ticks all the right boxes. Edinburgh is an extremely attractive proposition to terrorists as it has many international businesses, an airport, sports stadiums and crowded streets.

"Last year's Glasgow airport attack proved Scotland isn't immune to the threat of terrorism."