Can be a pita job Andy,
The obvious thing are:
1. The wheel is wonky.
2. The wheel supports are bent, twisted or both.
3. The inner shaft is bent.
4. the outer shaft is bent (kinda unlikely though).
1, 2, and 3 could have occurred simultaneously in a hard contact with something erm - harder.
Take the lot off the draw-bar, get it on a bench and straighten (you may need a lot of heat), if it is only a dodgy wheel then your luck is in and cheap to fix.
Saying that, if several components are collision damaged, the time put into repair may not be worth cost of replacement.
The cheap ones sold by some caravan dealers are poopy poopy wastes of space, good ones can be had from £45.00 by careful shopping around, check out the ones for commercial trailers e.g. Ifor Williams, Bateson and Indespension etc.