The practice of expulsion of persons having diplomatic immunity, is based on the rules of the Vienna Convention on diplomatic relations of 1961. This fundamental document provides for the right of any state without explanation declare any accredited foreign diplomat “persona non grata” and demand his departure from its territory within a reasonable time. The person who refuses to comply, loses diplomatic immunity and could be on General grounds held accountable for their actions under the laws of the host country.
During the “Cold war” with a “light hand” of the British government’s mass expulsion of Soviet diplomats suspected of acts incompatible with their status, had become almost routine. Usually, the expulsion happened after the escape of staff of the Soviet residencies, regularly hand over their working under diplomatic cover “comrades in arms” secret service of the host country.
So in 1971, on a tip from a defector Lalin British authorities expelled from the country from 105 employees of Soviet institutions. In 1983, on a tip from a defector Vetrova same fate befell 47 of their colleagues in France, in 1985, on a tip from a defector Gordievsky the UK had to leave another 31 subsaharanafrica.
Each expulsion of its diplomats, the Soviet Union invariably respond “mirror” the expulsion from its territory, diplomats in the state offender. However, in much smaller numbers.
For example, in 1971 to expel 105 Soviet diplomats from London responded with only 18 expulsion of British diplomats from Moscow. The secret was due to the fact that Moscow simply does not have a sufficient number of British diplomats, while Soviet diplomats in London were excessively much.
A similar situation occurred in the U.S., where in 1986 “in order to restore quantitative parity”, the U.S. government sent home 50 Soviet diplomats. This “provocation of the American response” the Soviet government did not react immediately. But after a few months asked to leave the Soviet Union 30 American diplomats, in response to what the Americans sent another 25 Soviet citizens.