Not very familar with that area but it sounds like apart from the zone transit you'll be in G airspace the whole way?
so no one you need to speak to. So no right answers in fact. The thinking should be - who can I talk to that will give me any kind of traffic service. No point in talking tp london info, they have no radar, so think about who can offer you radar coverage as the starting point, along with whos traffic you might be conflicting with. Also see if any of the available radar services publish a listening squawk, That's also useful. Does that help?