[3] This combination came about as early clockwork mechanisms and electric motors were difficult to fit within HO scale models of British trains, which are smaller than their European and North American counterparts.

Trix decided to use the new HO standard, being approximately half of European 0 gauge (1:43 scale).

In 1938, the Meccano Company launched a new range of OO models under the trade name of Hornby Dublo.

Soon other companies followed but it did not prove popular and remained on the market only until 1942, when Lionel train production was shut down due to wartime restrictions to the use of steel.

OO remains the most popular scale for railway modelling in Great Britain due to a ready availability of ready-to-run stock and starter sets.

Other scales, with the possible exception of N gauge, lack the variety and affordability of UK ready-to-run products.

Overhang from long vehicles means that the normal separation between track centres are overscale to prevent collisions on curves between stock on adjacent lines, at up to 65 mm (for set-track (reduced down to 50 mm for Peco Streamline)).

EM gauge has slightly overscale flanges and flangeways on point and crossing work; P4 is closer to scale but the smaller flanges and flangeways on P&C work expose poor track construction.