I am researching for a monograph which includes a brief description of the early National Grid. Does anybody know what voltage the early consumers received, 240V/415V 3-phase, or 230V/400V 3-phase?

I thought that it was 240V/ 415V 3-phase, but I have a 1930's 3-phase 40kW transformer designed for a primary voltage of 400V.

The origional Grid voltage was 132KV. The purpose of the grid was to link independant supply companies so that more efficient use could be made of generators.
The supply companies used various voltages both AC and DC. Right up to the 60's non standard voltages could be found. To this day non standard voltages can still be found on larger premises if there is an old agreement.
To begin with the main Grid company was the Central Electricity Board (CEB) It was much later that generation was included and it became CEGB.
The first part of the grid network was energised in I think 1931 between Portobello in Edinburgh and Grangemouth. The English network was energised the following year although the two contries networks were designed to be interlinked from the start.
I have a book published in 1985 which gives a short history of the English grid system called Power to The People by Rob Cochrane It was published by the CEGB. I dont know how available these books are but if it helps I may be able to lend you this copy.

Many thanks Arthur, there appears to be a copy in the IET library!

David