I understand that the UK issues a "Visitor in Transit" visa that is valid for 48 hours. But my question is whether the Visitor in Transit Visa is also issued in a "multiple entry" flavor so that it covers transiting via London on a "round-trip".
Haven't you already asked this question and had it answered?
Again, this page from the UK gov't website should provide you with advice and if you are still stuck on specifics to yourself you really should be reaching out to the UK embassy or consulate.