British Airways wanted their aircraft back in LHR as soon as possible, due to the aforementioned delays. BA had already cancelled flights for later on in the day. One of these cancelled flights was the early afternoon LHR-LBA rotation. So not only have they not taken you anywhere, they've cancelled the next flight to your destination.
MAN was asked by BA Operations to accept the divert and bus the passengers, so was likely the Captains decision to return to LHR.