Hi Sue!
Separation Anxiety - what a nightmare in two words!!
Sophie suffered terribly from it when I first got her 3 months ago (she is 6yrs old).
I had to do relentless training everyday, going out for 2 mins, then 1 min, then 5 mins just randomly so the dog has no idea how long you are going to be away.
Pick up keys when you are in the house, then put them down again - so that the dog does not associate the keys with you leaving.
There are all sorts of other things you can do - but it is hard work. But, even though Sophie still panics when I am at work, she is no longer a velcro dog when I am at home. In fact, she will come through to her bed (which is in my room), but during the night sometimes disappears through to the living room where her crate is to have a snooze - by herself!! Something that I would never have thought possible at the beginning when I honestly thought that Sophie was going to give herself heart failure or something as she was so worked up everytime I left the house.
I would recommend getting a DAP diffuser or spray from your vet though, just as an aid while you are training.
Feel free to PM me if you want any more info or a chat - SA Cocker mothers unite!!