The 1979 Act applies to England, Scotland and Wales and now, 40 years after its passage, has been amended extensively and by all three nations.
Mae Deddf 1979 yn gymwys i Gymru, Lloegr a'r Alban ac erbyn hyn, 40 mlynedd ar ôl ei phasio, mae wedi'i diwygio'n helaeth a chan bob un o'r tair gwlad.