Our Springer and Cocker have a kennel in the garden, a 10' x 9' shed with a 10' x 8' run in front. The Cocker lives out there at night (Springer in the house!) and they both spend time in their during the day if we are out, and after they have been walked or been working. They are fed there too and are both seemingly happy. When we shut the back door and say "kennel" they run in there and settle down happily. On just one day a week I work from 10 - 4 and they are left for this period after a good long morning walk. It has been tactfully brought to my attention that the Springer has a tendency to howl during the day. He is always happy to see us when we get in, but I have never witnessed the howling myself. He never ever barks (although he can) and certainly doesn't appear to be distressed in any way but obviously I don't want to upset neighbours.

Working on the basis that this is not behaviour that is witnessed, I am lost as to how to improve/correct it. Any suggestions most appreciated. Thanks.

You're lucky to have been told tactfully! So on the same token we must try to stop this. WQere you told that he howls at any particular time? There may be something that disturbs him (I have recently discovered that my lot howl like a pack of wolves when the phone rings more than 5 times.....). Can you rig up a tape recorder or video camra to try to find out what happens when you're out? Until you know the cause of the problem you won't be able to cure it.
:)