railways of Great Britain were formed into one or other of four new larger companies, in a process referred to as the "grouping", following the Railways Act 1921. The Brecon and Merthyr Railway was a subsidiary of the new Great Western Railway; the change took effect on 1 July 1922. There had, of necessity, been capital reconstructions in 1882 and 1902. In the twentieth century interest was paid on preference shares, and in 1918 – 1921 this was as high as 4%, but on preference shares only. At 31 December 1921, the B&MR had issued capital of £2.07 million; net income in 1921 of £66,577; dividend in 1921 on ordinary shares: nil; locomotives taken over by the GWR: 47; number of passenger carriages 90; number of freight wagons 640; employees 842. Single track mileage was 82miles-44chains en route mileage of 59miles-66 chains. From 1923 Many of the ironworks of the Merthyr and Dowlais areas were declining steeply or indeed closing in this period, and the B&MR network's dependency on those industries made it extremely vulnerable. A traffic pooling arrangement for mineral traffic between the GWR and the London Midland and Scottish Railway was agreed in 1933, and this resulted in a switch for much traffic to more efficient routes, avoiding the long and difficult climb through the Brecon Beacons and Talyllyn, and this reduced the volume of traffic. The hillside above New Tredegar had shown itself to be unstable resulting in temporary closure of the line in 1916, and more serious slips took place in September 1928, April 1929 and April 1930. This resulted in the closure of the upper portion of the branch from 14 April 1930; the only working colliery on the affected section could equally well be served by the former Rhymney Railway branch. From 1948 Under British Railways ownership after nationalisation, the decline in use of the railway continued, affecting all classes of traffic. The passenger service between Dowlais Central (the former B&MR terminus at Dowlais) and Pant was withdrawn from 28 June 1952. For a period workmen's trains continued but these were ended on 2 May 1960. The Machen to Pontypridd passenger service, instituted but not worked by the PC&NR, was closed down on 15 September 1956. The Merthyr to Pontsticill service was withdrawn from 13 November 1961 and the main line service from Newport to Brecon, and also the New Tredegar branch closed from