Thanks for the replies - after reading the signs of separation anxiety I'm not convinced that's what it is.... only one or two points out of all of them actually apply to Dougal.

Someone told me about practicing NILF - which we have now started, so we'll see if that is any help. I heard somewhere that if the dog thinks he's the alpha in the house, he's going to be upset when you leave because you don't have his 'permission'.

I think we're going to try getting a plastic crate and start slowly acclimatizing him to it.... I heard that some dogs are more comfortable in plastic crates?

That plug in looks great, thanks for the links!