fishing license

Hi all
I made a point about why do we bother we rod licenses a few days back, I
wasn't very clear unfortunately, my point is, on most of the fisheries
(especially here in south east wales ) they are mainly privately owned.
For example, we have Cefn Mably, Peterstone lakes and warren mill which are
pretty good venues.
Now with the exception of warrren mill, these lake were man-made by the
person who owns the land outright. They have made the lakes, stocked them
with fish at thier expense and the lakes are maintained by staff employed at
theses venues by the owners.
When you go there for a days fishing you obviously have to pay for the day
ticket, what I cannot see is why the EA have any right at all to go onto
this privately owned property and expect people to have rod licenses. This
means if I made a large pond in my own back garden, filled it with water,
kept it clean by using electric filters, then stocked it with fish,
according to the law I would need a rod license to fish in it.
I simply cannot understand the logic in this at all.
Clive