91.— (1) An authorisation comes into force on the day on which the authorisation is granted, or, if a later date is specified in the authorisation, on that later date, whether or not an appeal against any conditions of the authorisation is made under section 100.

(2) An authorisation remains in force, unless sooner revoked under this Chapter, for a period of 3 years from the date on which it comes into force.

(3) A reference in this section to an authorisation does not include a reference to an authorisation that is renewed under section 92.