Hornby Trains
Hornby O Gauge trains were first introduced in 1920. The product line was developed with varying levels of technical sophistication and relative costs associated. This meant that a child with 6 Shillings pocket money [£8.72 today], could afford to purchase a clockwork locomotive, tender, two Pullman coaches and a complete rail-set which could be infinitely modified. By contrast, a child with a significantly higher amount saved up could afford to purchase an electric version of the same locomotive for 5 Guineas [£152.55 today] in an elegant presentation box.
Later Hornby Dublo (00 Gauge) was made both 3 rail and 2 rail. It was developed so that model railways could be built in smaller houses as 0 Gauge took up a lot of space.
Here’s a link to a great Hornby 0 Gauge layout in operation via YouTube - Hornby 0 Gauge running layout
BBC Timewatch - This link is to a BBC TV documentary about Hornby Trains. Broadcast 23 May 1989. Note this video is the first part of a longer documentary.