MAN was asked by BA Operations to accept the divert and bus the passengers, so was likely the Captains decision to return to LHR.
Possibly so, but did MAN agree to accept the divert? It has a somewhat mixed record and unpredictable policy when it comes to taking diversions. Sometimes it's due lack of stands or the handling agents are short staffed. However, the BA shuttles from LBA are normally accepted. An Edinburgh shuttle came in quite recently.