Conditional exemptions validity limited to a two year term unless varied, with a transitional reckoning for existing exemptions. A new provision makes conditional exemptions under section 25(1) time-limited: they expire on the thirty-first March after a two year period from grant or variation unless otherwise specified, varied or rescinded. A transitional proviso directs that exemptions in force when the Finance Bill, 2021 receives assent have their two year period reckoned from the first day of February, 2021.