You are not allowed to pick, uproot or destroy any wild plant listed in
Schedule 8 of the Wildlife and Countryside Act 1981 even if it is on your
own land! You can of course with do what you like with any other wild
plant
on your land with the exception of bluebells which can't be sold.


Wow! That's the heck of a list!
http://www.naturenet.net/law/sched8.html
What's the position with things like pennyroyal which are commercially
available and that you may have planted in the first place?

" "wild plant" means any plant which is or (before it was picked, uprooted
or destroyed) was growing wild and is of a kind which ordinarily grows in
Great Britain in a wild state." (Section 27 Wildlife and Countryside Act
1981 )

Therefore any that you have planted yourself would not be considered wild.