Just go through the MCPS/PRS if you are in the UK.. You don't need permission for that one, but you need to protect the re-arrangement, by registering the title and the recording, which will have its own copyright and broadcasting right. If other songs aren't traditional that's a different issue. There are many publishing rights agents that can represent you worldwide and can deal with the agencies. Whoever is doing the re-arrangement will have rights to the work. Particularly if they are already a member of the PRS. Under membership rules a minimum writer's share is due when they register the work.   Whoever is the arranger, or their publishing rep. needs to register the work..and then there are cue sheets to fill in for films etc.