The June 1990 edition of Radio Communication, the monthly journal of the Radio Society of Great Britain, included an article entitled "UK licence amendments effective 1 June". Here is an extract from the article:
The July 1990 issue carried a little more detail:
Club Log maps all these prefixes to the relevant entity starting 1990-06-01. The only exception is GX, which does not require a prefix definition as it is mapped by the G prefix.
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