The information you need to reference correctly can be found on the title page of the standard.
FAMILY/SURNAME, Initials. (Year of publication – in brackets) Standard Number: Year. Title of the standard in italics. Place of Publication: Name of Publisher.
BRITISH STANDARDS INSTITUTE. (1990) BS5605:1990. Recommendations for citing and referencing published material. Milton Keynes: BSI.
In-text citation example:
(British Standards Institute, 1990)
‘Direct quotations are placed in single quotations marks’ (Author’s Surname, Year of Publication, p. – followed by page number – in brackets)