Aerad - Europe & Middle East Supplement volume
ATC Section
United Kingdom ATC Directory - National procedures
Ch. 6.4 - Speed restriction
"A speed restriction of 250kt applies to non-military flights below FL 100 in all classes of airspace except Classes A and B. (It also applies to IFR flights in class C airspace, but none is currently planned in the UK)
Exemptions will be granted for test flights, exibitions of flying and to aircraft that cannot operate safely below this limit".
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