Hi Guys. Had my email replied to today from the manager of Ribble Cycles.
From the images they are 99% sure it is just cosmetic. They said this area is the main junction and it is glued and wrapped with carbon to make the joint stronger than the individual components. They said this area has a lot or sometimes a little filler before the final coat is put on and is sometimes a bit inflexible. Either way, it has to flex with the frame and in rare occasions it can develop a thin cosmetic crack in the paint.
They have offered to exchange it but said if I wanted to ride it for the rest of the summer (as I have a major ride in 3 weeks) then just send them the frame and they are happy to exchange it when I am ready 🙂
Can't ask better than that?