Even if you litter on private land, you can still be guilty of littering if it can be seen from a public place such as a public road.
Extract from Litter Act 1997
Prohibitions related to littering.
3. —
(1) No person shall deposit any substance or object so as to create litter in a public place or in any place that is visible to any extent from a public place.
(2) No person shall—
(
a ) deposit any thing that is commercial, household, industrial or municipal waste in any place for collection by or on behalf of a local authority or by another person, or
(
b ) load, transport, unload or otherwise handle or process any thing or carry on a business, trade or activity
in such circumstances as to create litter or lead to litter in any public place or any place that is visible to any extent from a public place.
(3) No person shall place municipal waste into or near a litter receptacle.
(4) No person shall move or interfere with a litter receptacle that has been provided by a local authority or other person unless the movement or interference is authorised by the local authority or other person.
(5) For the purposes of
subsection (3), "municipal waste" has the meaning assigned by
section 5 of the
Waste Management Act, 1996 .
(6) A person who contravenes any provision of this section shall be guilty of an offence.