Personally, I dunno about 20lb. But it's quite beleivable I'd say.
I've certaintly seen a guy float fishing with a John Wilson Specialist rod, catch a very nice "Mid-Double" on Swim Stim Green Hook Pellet.
I stopped to chat to the guy because I recognised the rod, as I have a pair of them myself, it's while I/We were chatting that he caught the Mirror.
Superb rods BTW, 11ft 1.25lb "Avon" rods really, excellent for close in work.
Not that it really matters, but he was fishing on the last swim on the right, along the narrow bit that separates Spring from Heron (just at the point you turn Left to follow the "Far" bank on Heron).