Ihave a welsh springer spaniel who is 2 and a half years old, he has always been good when left alone, but I have just gone through a marriage breakdown and now every time I leave him he pees up against my curtains, chews up the rug at the door and goes absolutely mad at the back door can someone please help as I am in rented accommodation and I really don't want to get rid of him.

Dogs can sense when something isn't right, and they do pine for their owners when they leave.
If your partner is no longer living at home that can have a huge effect on your dog.

You can try separation anxiety training with him.
This just involves leaving your house for a very short period, just 30 seconds or a minute to start with.
Then each time you leave make it a little bit longer... so go for a minute and a half, and then 2 minutes, then 5, then 10 and so on.
This basically teaches the dog that when you leave, you will be coming back and that you aren't going to leave him alone forever.

When you leave do your usual routine. Pick up your keys, put your shoes on, make sure he knows you are preparing to leave as you normally would.

Always leave fresh water and just before you go give him a toy to distract him, kongs are great, they are a rubber ball that you can put food inside, the dog plays with it and occasionally gets rewarded by a treat falling out. (cheap alternative is a plastic soda bottle filled with dry food)

Making sure he is tired is another good way to help keep him calmer. A good long walk before you are due to go to work or shopping will help tire him out.

You can try crating as well, this will help with the separation anxiety. Some simple protocols for deference and relaxation should work as well. Like Shaz said lots of distractions, and the speration anxiety training methods will help a lot as well.