What it is
Deadbaits — smelt, herring, mackerel, sardine, lamprey, and the odd roach where rules allow — are how most UK pike anglers actually fish. You buy them frozen, thaw what you need, and fish them on a wire trace with proper unhooking kit.
Do not move live fish between waters. Livebaiting is banned or restricted on many fisheries; even where it is allowed, the bait should have been caught in that same water. This app recommends deadbaits and lures, not a bucket of someone else's silver fish.