The NER became part of the London & North Eastern Railway, as part of the 1923 grouping. Despite them having already begun to experience a decline in traffic due to competition from road transport, the LNER did provide some improvements to the line. One notable improvement implemented by the LNER was the electrification of today's DCL between Newcastle and Pelaw Junction, using the 600 V DC third rail system, as part of an extension of the Tyneside Electrics system to , inaugurated on 14 March 1938. The other notable improvement during this period was the opening of additional stations at on the NER-built Seaham to Hart line in 1936, and at Seaburn on the former Brandling Junction Railway in 1937.