It employs around 14,000 people, roughly one-third of whom are crown servants working directly for the Foreign, Commonwealth and Development Office, either in London or abroad.
The remaining two-thirds are employed locally by one of nearly 270 British diplomatic missions abroad (such as embassies, consulates and high commissions).
This compares to the general civil service fast stream, also highly competitive, in which 9.1% of candidates were successful.
The first female ambassador to be appointed was Barbara Salt, to Israel in 1962, but ill-health prevented her from taking up the post.
Eleanor Emery was British High Commissioner to Botswana from 1973 to 1977, corresponding to an ambassador but within the Commonwealth.