The London Midland Region (LMR) was one of the six regions created on the formation of the nationalised British Railways (BR) and consisted of ex-London, Midland and Scottish Railway (LMS) lines in England and Wales. The region was managed first from buildings adjacent to Euston Station and later from Stanier House in Birmingham. It existed from the creation of BR in 1948, ceased to be an operating unit in its own right in the 1980s and was wound up at the end of 1992.
More information on the Wikipedia page [1].
Details of archives, held at The National Archives here.
The London & North Western Railway Society website is [2].