1974 commercial for British Gas
In the early 1900s the gas market in the United Kingdom was mainly run by county councils and small private firms.
In 1948 that all changed with The Gas Act 1948 brought in by Clement Attlee’s Labour government. The act nationalised the UK gas industry and 1062 privately owned and municipal gas companies were merged into twelve Area Gas Boards each a separate body with its own management structure. Each Area Board was divided into geographical groups or divisions which were often further divided into smaller districts. These boards simply became known as the “Gas Board”, a term people still use when referring to British Gas.
Info gleaned from Wikipedia