Kim,
If I get the time, I'll try and dig out my reference which was a long article in Your Model Railways many years ago which recounted the development of British railway modelling.
Immediately after WW2, the BRMSB (British Railway Modelling Standards Bureau) was keen to evaluate and set up new standards for railway modelling - in effect, drawing together and rationalising the various threads of development which had been going on before WW2. I think they had the example of the NMRA in North America and what it had set about to do to bring some semblance of order to the North American modelling market.
The long break in toy manufacturing caused by the war could have given a clean slate to start over again with fresh ideas, but for whatever reasons, Hornby decided to put their old production line back into operation with exactly the same standards as they had used pre-war. Since they were the leading British producer at the time, that virtually decided the standard and the BRMSB didn't have the teeth to push for anything much different.
They did bring out the BRMSB 00 standards which were not the same as Hornby Dublo, but the HD standards were included in their set of standards. Trix came back into the market with their very coarse standards and Rovex(Triang) came into the market with their own coarse standards. The only manufacturer who produced to BRMSB standards in
4mm scale was Graham Farish.People were looking to widen the gauge of 00 at that time, and EM (Eighteen Millimetre) gauge came into existence and was included in the BRMSB standards as well.. Maybe if BRMSB had had their way, EM would have become the accepted gauge for 4mm modelling in the UK - being a fair compromise between gauge and width over wheels (see Martin Wynne's post on the practicalities of gauge and wheel widths.)
Jim.