As a pretty much outsider to this too (apart from knowing an ex-colleague who I expect would quite like to know what is happening to the company he currently works for), I find this rebranding mullarky quite baffling,not to mention a presumably large waste of scarce aviation money spent on endless aircraft repainting, advertising and consultancy fees. I think it's reasonable to expect that if you took a straw poll of Joe Public and asked them if they knew who Brittania as a brand was, compared to TUI, it's a safe bet most people would think Brittania was/is going strong in it's own right, and not know who the hell TUI was. I'm not saying don't refresh and innovate, but if you must do it......
.......do it right, do it once, explain it effectively to all your staff on the Monday and then launch in a blaze of publicity on the Tuesday.
If I ever call my ex-colleague at work I always refer to him at Brittania, never Thompsonfly, primarily because when I say 'Brittania' people know what/where/who I'm on about.
My 2p.