Thanks so much for that advice Vintage Diva.
I went back to work today and it went really well. I tired him out in the morning and he slept, so I left when he was asleep. I checked on him late in the morning and gave him his Kong and then again in the afternoon and gave him a chicken neck. I waited outside each time I left and he didn't cry. He had lots of toys and the Tv left on.
They only thing was that each time I came back he was so sad, crying and running with his tail between his legs and wanting a cuddle, then to get down, then a cuddle . . . but I guess he will get over that. Luckily I work across the street from home and have 2 breaks, so he is never alone for too long.