The first effective co-ordination of the electricity supply industry came in 1926 with the Electricity (Supply) Act, by which the government established the Central Electricity Board. The Board was a public corporation and built and ran the National Grid of main transmission lines. Electricity generated at selected power stations could be supplied wholesale over these transmission lines to local distributors for sale to customers. Individual undertakings continued to own and operate the power stations and sold their electricity to the Central Electricity Board. By 1934, the National Grid system was serving most parts of Britain. A Government White Paper issued in 1937 proposed that the Electricity Commissioners should prepare schemes for the integration of distribution undertakings into larger groups, but the Second World War prevented legislation.