britanniaboy
I am sorry to point out a slight error in your post.
I quote "(there is still, at the moment, some distinction betweeen the two within the company, but it is one airline)"
It is still two Airlines, it's not the paint scheme that matters, it is what is on your AOC.
Until it is changed by TUI and submitted to the CAA, it remains Britannia and Thomsonfly.
However l would guess, that this might happen for the 1st November.