As others have pointed out above, the garden railway scene in the UK is dominated by 16mm scale/32mm gauge which well suits small British 2' gauge rolling stock in small British gardens. There is an absence of suitable (non-tramway) prototypes on 3', metre or 3'6" gauge in the British Isles. The glaring exception is of course the Irish 3' gauge lines which seem to have a very limited following in this size, surprising considering the abundance of very attractive prototypes and the extensive trade support for IoM railways. However, the British built many railways outside these shores, and a great number of these were narrow-gauge. This includes enormous metre-gauge networks in India, East Africa, Argentina and Brazil, and Cape gauge systems in Southern Africa, New Zealand and Australia. Even in Europe, there were substantial British owned narrow gauge operations - the Rio Tinto railway had a roster of 150 steam locos including two Garratts.
So there is a huge number of British prototypes suitable for G "scale" from the drawing offices of Beyer Peacock, North British, Vulcan Foundry and the rest, plus an amazing variety of rolling stock. As a bonus, 45mm gauge is spot on for 3'6" prototypes at 1:24 scale, so it's very easy to translate imperial measurements from drawing to model.