There can't be many waters that DON'T hold a 20, especially the gravel pits round your way, Glider. The fact that you've 'only'# caught a 16 (and that's a damned good fish, by the way) doesn't mean there are no 20s in the water.
I don't know if Broadlands is still a goer - old Bloater Simmonds used to stuff it with culled grayling every year, and the pike got as fat as he was.
But seriously, choose any gravel pit and ring the changes - drift some deads, leger big baits, sink-and-draw at dawn, do the lot. Piking has always been a bit of a numbers game, but the usual form is - as with most specimen fishing - to do what hardly anyone else is doing, and at different times.
You'll get your 20 if you persevere instead of dipping into a different water each day.