I used Triang which was two rail, Hornby was three rail, seem to remember trix made universal track which could be used on either, and latter the two firms combined. The old Triang had a special rail to connect with. And seem to remember the old Hornby was the same.
But there were also different gauges, OH I seem to remember was mine, but sister had TT, and she also ran off with my clockwork set which was much larger and was also Hornby.
I have grown a bit older not and play with 2'6" set, 8 miles long, can't drive the engines, not sure I want to, it's hard work. 50 minutes end to end, but also some 16 gauge, at the moment inaccessible due to new roof being fitted, but should have two sets running my next year.
Too expensive to own my own, one guy has a model Garratt the wheels alone cost him £1000, don't think my wife would allow me to spend that. Next door is setting out 16 gauge in his garden, but really part of his job, he writes for the magazines, so he needs first-hand experience. But not seen an engine run yet.
But here in Wales we have lots of little trains.