Dh actually found him, in the village, limping badly and with obvious cuts. The dog was entirely docile and let dh pick him up and put him in the car.
We've brought him in and made him comfortable on towels, and have rung the SPCA for advice etc. Plus we have taken photos and will put them on fb to see if we can trace an owner.
He has been offered, and has rejected, a few bits of dry food and some water. We are going to give him a gentle wash with warm water and a bit of dettol - is there anything else we should do?