Ok maybe this has been answered but heres my 2 cents.
Yes, catching good size Tench is possible, even in the middle of winter. Although there are some tricks you need to know.
First of all is the location. You need to find a small pond that holds a good head of Tench. Big gravel pits and lakes wont work. A small mill pond or something, with a decent margin and overhangs etc. Once you find your target lake, then choose 1 swim that you are religiously throughout. Now heres the trick, feed this swim up as often as you can, even on days your not fishing. Picking a local pond is good because you can easily find the time to visit and pre bait when your not fishing. Eventually fish will find the swim, and, if you keep the food going in they wont move off to much and will also keep feeding. You have to remember that fish feed less in winter not becuase there not hungry, but because there are using more enery keeping warm. If they can find a good supply of food, with little effort, they will feed and continue to feed until the food stops.
Ive been feeding a swim throughout October and yesterday (Nov 1st!) had a 7,7lb, fin perfect Tinca and ive been on today to feed up and there was plenty of bubbling.
Do this and i promise you will catch tench all year round!