Where can you get pickerel?well I'm guessing, like dive said, you mean a northern pike right? Unless the uk has a species I'm unaware of , they should be the same thing as we have here.
Like ALL esox species, smaller tank mates are a no go. Anything that pike THINKS it can fit into its mouth it will try. Also as Dive said these fish get pretty large, much to large for standard aquariums. I keep pickerel, the mini version of a pike, but I've never kept a true pike before...not yet anyhow.