Thanks for posting this Philip. My wife and I don't get to go across the pond as often as we'd like, but when we do, attending the Ffestiniog Victorian Weekend is a highlight. "All the toys out of the box" as they say. And since the railway is literally the birthplace of narrow gauge, it's a must see.
When you were there in 2017, was it for the Victorian Weekend? If so then it's a small world, because we were there too. Here's a couple photos.
The first shot is of "Prince", one of the line's original locos from 1863.
The next shot is double Fairlie " Merddin Emrys, from 1879
Then we have single Fairlie "Taliesin", built at the railway's Boston Lodge Works in 1999.
Inside Boston Lodge Works, which is the oldest continuously working locomotive works in the world. And they're building another double Fairlie right now. Fantastic stuff.