G-TUIB and G-TUIH have been reconfigured for 325 seats for approx 6-7 weeks for shorthaul ops over july/august. It takes approx 1 week of hangar work to rearrange all the seats/wiring/PSU etc.
G-TUII was delivered with 300 seats which will be the new TUI group config, so by the end of winter 15, ALL the Thomson 787s will join the Arke and Jetair 787s as being 300 config. This allows the group airlines to use any other 787 if they wish, as the internal layouts will all be the same.
I have said before that NO one plane (737/757/767/787) is ever "based" at 1 airport. The planes are swopped around usually abroad. Over the last few years, the 6 week summer period (jul/Aug) has meant some strange aircraft basings, like 3x767@Man, but the other morning, LGW had 5x787!!!