A father of three daughters and one son, Mr Scarlett, 45, joined the Foreign Office in 1971 and within two years was working as a third secretary in Nairobi.
After a spell as a language student, he was posted in 1976 to Moscow, where he was promoted from second secretary to first secretary. However, this assignment proved to be unusually short. Most diplomatic postings last for several years, but by 1977 Mr Scarlett was back in London.
If he was already working for MI6 at this stage, this may explain the brevity of his first stint in Moscow. Either the then Soviet authorities may have suspected the nature of his real duties, or his masters may have decided to limit his spell in Moscow for other reasons.
According to the official Diplomatic Service List, which records the movements of Foreign Office staff, he was not assigned abroad again until 1984, when he was posted to Paris. Three years later, and before he had even reached his 40th birthday, Mr Scarlett was awarded an OBE.
The fact that he received this honour when he was still only a first secretary - a respectable but middle-ranking position - suggests that he may well have been performing other services that merited official recognition. In any event, he returned to Moscow in October 1991, just before the dissolution of the Soviet Union.
Foreign correspondents in Moscow who mix with British embassy staff at diplomatic functions and other social occasions say they cannot recall ever having met Mr Scarlett. This in itself proves nothing, but it is rather unusual in the tightly knit foreigners' circles of Moscow, where most people get to know each other very quickly.