asked Her Majesty's Government:When they decided that membership of a trade union was incompatible with work at GCHQ and what incident or incidents convinced them that this was so.

:Since the disruption of work at the Government Communications Headquarters caused by industrial action between 1979 and 1981 we have been considering what steps were required to prevent any recurrence. We reached the conclusion that measures should be introduced which would have the effect of prohibiting the staff of Government Communications Headquarters from belonging to a trade union other than a departmental staff association approved by the director. This decision was announced on 25th January 1984.