Never heard it been called walkmill always known it as rosemary tiles it's not easy really deep even the margins are 20 ft around 60ft in places good floater water if you persevere used to be free fishing until around 5 years ago majority of anglers really struggle no point in poaching it as you need to put the time in and you will get caught. This thread been going a while surely you been into local tackle shop and asked them about it?
Used to be dodgy down there don't no what it's like now but with the gate been locked should be better. Used be some stunning fish mainly doubles and 20ties and few low 30ties and of course the big myth common l. Pretty sure with bit of effort you could get on.