So where exactly is the Birches Green Light Railway set? It is not actually prototypical to Birches Green in the UK which has no railways (well the Birmingham-Leicester line might just scrape the edge depending on where you draw the ward boundaries).
When I re-started railway modelling several years ago I went for HOe narrow gauge and rolling stock from the Austrian Zillertalbahn railway. Later on I got rolling stock from other Austrian narrow gauge railways, and some German wagons. I've also got an East German locomotive. So I suppose Birches Green could be some kind of preserved narrow gauge railway somewhere in Austria. It doesn't really matter, the main point is to enjoy what you are doing. Seeing lovely locos like Maggie and the Falcon pass by makes it all worthwhile.