4(1)The carrying out, on land which was used for the purposes of agriculture or forestry at a material date, of any building or other operations required for the purposes of that use.
(2)Sub-paragraph (1) does not apply to operations for the erection, enlargement, improvement or alteration of dwellinghouses or of buildings used—
(a)for the purposes of market gardens, nursery grounds or timber yards, or
(b)for other purposes not connected with general farming operations or with the cultivation or felling of trees.