From the vintage pile today, we have this interesting vacuum-formed tunnel mouth and wing-wall set from Thornton Mfrs (Harrogate) Ltd, based in Long Street, Easingwold, York. A quick look at the street in Google Streetview doesn't show any obvious manufacturing places, but then a vac-forming machine isn't huge so you don't need more space than a garage.
The name suggests to me that this was a sideline from a larger manufacturer. It's certainly not a snappy title!
The sheets themselves aren't bad. The forming is nice and clean and I'd suggest the master was carved judging by the shape of the brisks. It's a pity the bond is stretcher rather than something accurate, but I've seen worse.
Sadly, this is all I know. If anyone can fill in some history for the firm and any other products, please comment away below.