This is very straightforward. It's all in the same Terminal T1 and there's a dedicated international to international transfer which you can't miss upon arrival from MNL. You don't have to go landside and your bags will be checked through to LON. This is assuming, all your flights are on the same ticket and are all MU flights. If you'd be on PAL from MNL to PVG, you'd have to change terminals and self-transfer your bags.