Spent 30-odd years driving through the night on routes all across England and Wales and I'll tell you, you see things in your headlights that the daylight crowd never get to witness. Big cats are real, full stop. The number of times I saw something cross the road that was absolutely not a dog or a fox, and far too big and low-slung to be anything domestic.
The Shropshire hills area doesn't surprise me at all. Plenty of cover, decent prey population, keeps itself well away from people. That's exactly the behaviour you'd expect from a melanistic leopard or a puma that's been out there a generation or two.
What time of day was the sighting? And roughly which part of the hills - Long Mynd area, or further toward Wenlock Edge? The details matter more than people think. Track width, gait, tail length relative to body. If anyone got a photo I'd really like to look at the pixel data properly before anyone starts crying "big dog."