Hi there!
I am delighted to report that Harvey brought himself home last night! We spent the evening walking the neighbourhood with leaflets, jangling his ball toy with a bell in the middle, and calling his name, to no avail. We also left a bowl of food in the back garden, as suggested by yourselves. My partner and I had resigned ourselves to a sleepness night worrying about our little Harvey, and then we heard the cat flap click - and sure enough he bounded onto our bed and showered us with nuzzles and purrs. As you can imagine we were overjoyed, although we will never know where he had been, or whether it was the food which enticed him home, or perhaps whether one of our leaflets prompted somebody to check their shed. My partner and I, and our other cat Misty, are just very very glad he's back home, and I wish the same luck to everybody whose furbabe has gone awol.
Many thanks for the excellent advice and support from this site, and good luck to those still searching.
Jenny
xx