The following quote is from the commentary to the Local Council Library, Encyclopaedia of Planning, Law and Practice. (Release 101;14-ii-92)
Page 38125 paragraph 3B-1123

(4) placing structures on agricultural land
The breadth of s.55(2)(e) also means that structures may be placed on agricultural land for, agricultural purposes without there being any “development,” provided that no building or engineering works are involved. In order to attract control, it would be necessary to show that there had been a material change in the use of the land. But the act of placing a structure on the land does not in itself constitute a material change in the use, notwithstanding that it may be inappropriate both in function and design for agricultural use. Thus a residential caravan placed in a field attracts no planning control so long as it is put to an agricultural or ancillary use (Restormel Borough Council v. Secretary of State for the Environment and Day (Colin) [1988] J.P.L. 268 (C.A.)). It, may, for example, be used for shelter for animals on the land; or, to use some examples suggested by the Court of Appeal in the Wealden case (at p. 277), to provide shelter for farmers or employees running “pick your own” ventures, storing and mixing feed, some related office work or the taking of shelter. The Court rejected the submission that a residential caravan, because of it’s nature and ordinary use and associations, had to be regarded as incapable of being incidental to a primary agricultural use.


  Mr. Avery pointed out that the foreshore may not be interpreted as agricultural land. Presumably he meant ‘agricultural land ‘ as defined in Class D of part 6 permmitted development rights as refered to in the Town and Country Planning (General Permmited Development) Order 1995.
Note that where planning controls may be exempt or permiited development rights exist regarding ‘agricultural land’ this must refer to the statutory definition not a casual reference to land that is being used for agriculture.
a)    ‘Agricultural land’ as defined in the GPDO part (6) Class D1 as land being used for the purposes of a business or trade, is not the same as;

    ‘agricultural land’ in the quoted commentary in schedule 2 above......  note the commentary to s.55 (P55.32) page 2-3173 Planning R.112 September 1995 of the Encyclopaedia, or
    use of ‘agricultural and forestry land’ and buildings

here agricultural land does not contain the restriction of trade or
business, and on  page 2.3174 is stated
“The definition is broad and it encompasses the use of agricultural land for the purposes of allotments.......(hardly a trade or business)
the term agricultural land here has a different
meaning to that of Class D1
a/ Class D1 (agricultural land), is a legal definition in statute
b)    ‘agricultural land’, mentioned in the commentaries, is an grammatical alternative of  ‘land used for agriculture’, whether or not it is for business.

hence the placing of a shed for tools or a ‘small’ movable cloche, cold frame or greenhouse would not constitute development when used for agriculture on an allotment.
If for some seemingly obscure reason the LPA wish me to move the boat as
it makes a material change in the use of land, I state again

yours sincerely,

  Mr. Avery pointed out that the foreshore may not be interpreted as agricultural land. Presumably he meant ‘agricultural land ‘ as defined in Class D of part 6 permmitted development rights as refered to in the Town and Country Planning (General Permmited Development) Order 1995.
Note that where planning controls may be exempt or permiited development rights exist regarding ‘agricultural land’ this must refer to the statutory definition not a casual reference to land that is being used for agriculture.
a)    ‘Agricultural land’ as defined in the GPDO part (6) Class D1 as land being used for the purposes of a business or trade, is not the same as;

    ‘agricultural land’ in the quoted commentary in schedule 2 above......  note the commentary to s.55 (P55.32) page 2-3173 Planning R.112 September 1995 of the Encyclopaedia, or
    use of ‘agricultural and forestry land’ and buildings

here agricultural land does not contain the restriction of trade or
business, and on  page 2.3174 is stated
“The definition is broad and it encompasses the use of agricultural land for the purposes of allotments.......(hardly a trade or business)
the term agricultural land here has a different
meaning to that of Class D1
a/ Class D1 (agricultural land), is a legal definition in statute
b)    ‘agricultural land’, mentioned in the commentaries, is an grammatical alternative of  ‘land used for agriculture’, whether or not it is for business.

hence the placing of a shed for tools or a ‘small’ movable cloche, cold frame or greenhouse would not constitute development when used for agriculture on an allotment.