In this Part of this Act, except where the context otherwise requires—
(a)" mortgagee " and " mortgagor " include any person from time to time deriving title under the original mortgagee or mortgagor; and
(b)" legal mortgage " in relation to regulated mortgages, and " mortgage ", in relation to controlled mortgages, include any charge registered under the [1925 c. 21.] Land Registration Act 1925.