170.Under the TA 1985, permits granted under section 19 or 22 remain in force indefinitely until surrendered or revoked. The effect of subsection (1) (which inserts a new section 23A into the TA 1985) is to enable a date to be specified in regulations after which all such permits will be granted for a specified period, not exceeding 5 years. Subsection (2) enables regulations to provide for all permits granted before that date, and which were therefore issued on an indefinite basis, to be revoked. Holders of such permits would be able to apply for new time-limited permits to replace those revoked.