MR to BOM
 

I currently have flts on hold, BA arriving from LHR around midnight then departing a little after 2AM returning to LHR. Will I have enough time to make this transfer?

Should be no problems with the new terminal in BOM. If you can checkin for your next flight and have a paper BP handy it would be even better.

Still note that you have to have a visa for India, even if you don't intend to use it.

be prepared to answer a bunch of questions on why you are heading back immediately....the mr concept is pretty unknown to most agents in indian airports....