British Rail
From Festipedia, hosted by the FR Heritage Group
Over the years since the initial creation of the Festiniog Railway, the standard gauge railways have changed greatly.
The Aberystwyth and Welsh Coast Railway, created 1861, merged into the Cambrian Railway by 1867, which during the "Grouping" of 1922, was absorbed by the Great Western Railway.
The Festiniog And Blaenau Railway was a seperate narrow gauge operation, which extneded the Festiniog Railway 2 ft gauge to Llan Festiniog, operated from May 1868 to 1883. The Bala And Festiniog Railway, which had bought the F&BR in 1876, was a standard gauge line, that by 1882 had reached Llan Festiniog. The F&BR section was then converted to standard gauge and through running commenced September 1883. The B&F was already a puppet of the GWR and was eventually amalgamted to it in 1910.
The London & North Western Railway was the name for the interlopper at Blaenau Ffestiniog. In the "Grouping" of 1922, it changed to the London Midland Scottish (LMS)
In 1948, the railway system in the United Kingdom was nationalised and operated under a general banner of British Railways. With privatisation in the early/mid 1990's, responsibility for the infrastructure went first to Railtrack, a privatised operation, then Network Rail, a semi-governmental operation.
Under the 1993 Railways Act, the old British Rail was split up and sold off. By November 1997, British Rail had been divested of all its operating railway functions.
The remaining functions of the British Railways Board are now discharged by BRB (Residuary) Ltd. The company is owned by the Government and reports to the Department for Transport.
As a residuary body, the company is responsible for discharging a variety of functions, including obligations in respect of liabilities acquired by British Rail as a major employer over nearly half a century and as a direct result of the privatisation process.
The above 3 paragraphs are taken from the BRB site. However, I believe the "in respect of liabilities acquired by British Rail" would actually cover not only the period of BR's existence, but any liabilities prior to its creation.