Dear All, I am afraid that this is not that much to add to the already fantastic contributions regarding Metropolitan Machinist Company and Benetfinks but M.M.C.were trading in 1894 from 75-76 Bishopsgate Without, London E.C.4. This is well before the the 1920's/30's date mentioned. M.M.C. made the "Juno" bicycle which were sold from their shop at 168 & 248 Bishopsgate, London E.C.4. in the 1920's. They celebrated their jubilee year in 1927 so they were building in 1877. The best loved and known Juno model was their No.3 Road Racer.
Your fraternally Frank.
Frank Cohen Hoxton UK