Baby bird fallen from nest: ID appreciated

Please can anyone tell me what kind of bird this chick is? I found it this evening in my garden just before bedtime because my dog was sniffing excitedly at it on the ground under some large trees (too tall and dense for me to find a nest let alone replace the chick unfortunately. Its beak was gaping, and it wasn’t moving around on the ground, though it’s eyes are open and seems alert, so it’s still a nestling rather than a fledgling. I couldn’t safely leave it on the ground as my cat was nearby, as well as the dog (who is used to chickens so didn’t harm it) I’ve put in in a box with some straw on our heated bathroom floor overnight. If it’s still ok in the morning I’ll call SSPCA, though would like to know what it is and if there’s anything I can do to help its chances. Thank you.