PPRuNe posts suggest that there was a medical emergency resulting in a divert to BOS, where the aircraft was on the ground from 0338L to 0450L. The aircraft then continued to CWL arriving at 1550L. The flight appears estimated to depart CWL at 0630L tomorrow arriving at LHR at 0717L, but I suspect this will just be a ferry. The suggestion appears to be that the crew would have gone out of flight time limits if the aircraft had simply continued to LHR from BOS, thus requiring a divert to somewhere a little closer to BOS, but still in the UK. At a guess, coaches were laid on to bring the pax from CWL to LHR, with a change of mind somewhere along the line as to whether they'd go to T1 or T4.