I do have a 76 Midget and I did have an electric fuel pump connected thru the fuse block. There are a couple of things that I feel obligated to say...1. The answer given above is a good one, and your skematics in a Chilton or other aftermarket book are adequate to find a location to hook up a fuel pump (be sure the circuit can handle the amps that are being added along with whatever is on the circuit currently and do not just put in a higher amp fuse...the wiring will melt) and Victoria British has listed several books on MG/British Leyland wiring...BUY IT TOO, and 2. Be or become very knowledgable about wiring and electrical circuitry.. you own a Lucas product and I for one have been thru many headaches and spent numerous hours finding "gremlins" in the wires. MG/MG Midget/Triumph/Austin Healey/ etc are all linked by one common thing... Fragile and sensitive wiring.
However, I do not call it "bad" or poorly designed like I have heard from American Mechanics; but simply fragile, delicate, sensitive, touchy, and sometimes frustrating. Get some books, read, read, and then do ( like Bob Villa... measure twice and cut once). You really should have a relatively simple time adding an electric fuel pump...not a major project at all.