Three years on I'm finally making this trip, well on a slightly different route, and the same issue persists. I actually found my own thread through Google as I searched for answers!

Whilst happy just to pay the potential fee, I dont fancy being sent from check-in desk to another place to pay and all the hassles that potentially comes with needing to pay more at an airport.

Have decided to put a small carry on style case inside my larger case, and on the internal flights, I'll just use that as another hold bag. Might actually be handy having the small case for places I'm just staying one night.