no BA lounge (at least last time I was there) - is the Malaysian Lounge(s), subject to One World status and class of travel of course - BA website has full details or check-in staff will tell you
the Malaysian lounge (if not Gold / First) is fine - nice little bar area on the left as you walk in and quite big lounging area - can be crowded at that time of night as the Malaysian A380 for LHR leaves around the same time as BA - I didn't have much luck getting proper food there, but although departure time is late locally, it is a long flight so eating on the plane can be a nice way to ease back into UK timezone