# The Traffic Signs Regulations and General Directions 2016, Paragraph 2

Extent: E+W+S

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 for the purposes of indicating a temporary statutory provision, the following modifications to the requirements apply—
(a) the diameter of the circular sign must be at least 200 mm; and
(b) the x-height of the lettering on a plate where the legend is either “One way” or “End”, if used, must be at least 20 mm.

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Source: https://www.legislation.gov.uk/uksi/2016/362/schedule/3/part/4/paragraph/2 (the official version)
Page: https://openlegislation.uk/traffic-signs-regulations-and-general-directions-2016/schedule-3/part-4/paragraph-2
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.