http://www.legislation.gov.uk/uksi/1974/502/schedule/2/paragraph/23/made

The Motorways Traffic (Speed Limit) Regulations 1974

Westlaw

King's Printer of Acts of Parliament

2011-05-19

ROAD TRAFFIC

These Regulations re-impose a maximum speed limit of 70 miles per hour (in lieu of the 50 miles per hour speed limit imposed by the Regulations revoked by these Regulations) on the driving of motor vehicles on motorways, except on the lengths of motorway referred to in Regulations 4 and 5 (on which speed limits of 60 m.p.h. and 50 m.p.h. are respectively re-imposed by these Regulations) and except on other lengths of motorway which are for the time being subject to speed limits lower than 70 m.p.h.