You've not really clarified why your Scout Association membership was terminated (or if as you state, you don't know why, then you should follow it up)
This said, for a DEFAMATION of character lawsuit i suggest a preliminary chat with a solicitor (they will do this for free, before deciding whether you have a case, and whether they will represent you, as well as how much it may cost you). Mortartube has the right idea but it's usually best to leave it to the professionals, and the solicitor will rattle more cages than you will hope to