If you want UK native predators in a cold water pond then you're looking at pike or perch really. Zander aren't as widespread. Size wise, from a long term point of view, a pike may turn out to be a bad idea, depending on the size of your pond that is.
But perch on the other hand? You could keep a good sized group as they won't get that big in a pond environment, and the best thing is they are common throughout the UK, you can catch these guys as tiddlers easily in a local pond or canal.
You could feed them worms to begin with if you catch some small ones, and as they grow and their predatory instincts kick in, you could add minnows, small roach or rudd as food, again these are readily available in local waterways.
Where i live there are numerous small waterways where I could collect perch and feeder fish without too much trouble. Just be sure you check before you fish anywhere that you aren't trespassing!