Leading the tributes, Prime Minister Sir Keir Starmer said Sir Alex “led an exemplary life and career”, adding “he will be remembered by the many ministers, colleagues, friends and family for his utmost dedication to British public life and protecting our nation.”
Blaise Metreweli, the current chief of MI6, said Sir Alex “embodied my service’s values of integrity, courage, creativity and respect.”
She added: “He made a lasting and distinctive contribution to our country and indeed to global security”.
Sir Alex once spoke to his old university, St Andrews, about his first job in the western Balkans in the mid-1990s, paving the way for the prosecution of war criminals.
He later headed up counter-terrorism at MI6, with his role including preparations for the 2012 London Olympics.
In late 2014 he succeeded Sir John Sawers as the head of the Secret Intelligence Service, otherwise known as MI6.
At the time of his appointment he faced numerous challenges: frustrating any attack plans against the West by jihadists in the Middle East and elsewhere, monitoring and containing Iran’s nuclear ambitions, and trying to second guess Russia’s next moves in Ukraine.