The Traffic Signs Regulations and General Directions 2016 No. 362

SCHEDULE 11 Signs that give information, are advisory or guide traffic

PART 6 Requirements applying to signs in Parts 2 and 4

1.  Where the sign is placed temporarily on a road by a constable or person acting under the instructions (whether general or specific) of the chief officer of police in connection with a temporary statutory provision, the diameter may be reduced to not less than 200 mm.