In reply to russellcampbell:
As regards your car you've got no right to park it on someone's land without permission.
But if you are walking on a path on the O/S map which goes through a farmyard and they've not provided an alternative you're following the code and they shouldn't be hassling you.
"Although access rights do not extend to farmyards, many people take access through farmyards when following paths and tracks.
In practice:
if a right of way or core path goes through a farmyard, you can follow this at any time
if a reasonable, passable alternative route is signposted around the farmyard and buildings, then you should follow this.
In the absence of a right of way, core path or reasonable, signposted route around the farmyard and buildings, you:
might be able to go through the farmyard if the farmer is content or if access has been taken on a customary basis in the past; or you
could exercise your access rights to go around the farmyard and buildings."