4. The amendments made by regulations 2 and 3(2), (3) and (4) of, and the Schedule to, these Regulations apply only in relation to a voucher—
(a)accepted or used on or after 1st April 1990 pursuant to regulation 12 or regulation 18 of the principal Regulations; or
(b)sent to a Health Authority pursuant to regulation 14(2)(c) of the principal Regulations in respect of cost incurred on or after that date.