The maintenance of ground by the council of the borough of Worthing shall not be treated as a defined activity so long as—
(a) it consists of the tending of any tree having a stem circumference which, if measured at one metre above ground level, exceeds 350 millimetres; and
(b) it is carried out—
(i) before 1st April 1997 at the Hillbarn Golf Course or in the Central, Goring, Heene, Marine or Selden wards; or
(ii) during the period beginning with 1st September 1996 and ending with 31st March 1997 in the Broadwater, Castle, Durrington, Gaisford, Offington, Salvington or Tarring wards.