Thanks. I just called the emergancy Vet in Edinburgh and they told me to watch for vomitting and diarrhoea over the next 5 days - in which case he will need to be treated and tested for related problems. Told me I'd been stupid and hopefully he'll be ok - keep him hydrated and little food portions at a time.
He's just had a bowel movement - all was fine. He was also just chasing a cat in the garden. Hopefully i'll be lucky, but I'll monitor him closely.