Theres a Giant Mutant Monster lizard in my garden

I was getting coal from the bunker when I found this on my shovel - lucky I didn't slice it in two.
It seemed stunned rather than dead so I put it near the pond and it was gome 30 minutes later.
Hopefully for a long fulfilling (for a newt) life rather than lunch for something else - that may also be having a long and fulfilling life.

If anyone can tell me what it is, why it was in my coal bunker and if I'm likely to find more, i'd be grateful