does anyone know why it returned?
Actually yes I do, but I'm not telling ( more on that in a moment)....and I'm siding with H.T.
Why not just chalk it up to an airborne return, which, given the time scale, wasn't something urgent/life threatening? It might be down to a whole host of reasons. FWIW if you're looking for info from those who have access to in house information they are sure as heck are not going to post it here.....
That said chances are one of the BA info websites may well have the information in the near future.
NS
and the logistics of such a return would be of interest if, for instance, A/C weight was an issue. Four hours 'burn' may not be in this case.
NS
In answer to that question the likes of a 777 or 744 can, even after 4 hours in the cruise, be well over maximum landing weight..the answer to that problem is usually to dump fuel, rather than just flying around to burn the fuel off.