Any shells which walk rather than slide probably contain a hermit crab, they tend to adopt spiral whelk and winkle shells as homes.
There are many different types of hermit crabs which can occupy almost any size of shell you might find. When startled they can withdraw into their shell if it is large enough - where a mollusc has a wet circular foot hermit crabs have 8 pointed legs and two pincers which sometimes interlock to form a door. The small ones can't easily be told apart, but large ones (more than 20mm long) are Pagurus bernhardus.