Thanks for the advice guys!
The howling at night has now stopped thank god! With the help of a kong and a small night light being left on.
A stairgate is now in situ so we dont have any hairy invaders other than the cats during the night and we are now looking for a friend for Charlie so he doesnt feel so anxious in the day time.
We have started leaving the tele on during the day and when we return he is calmer but he does still howl at times during the day according to the neighbours so i think i friend might help!
He is also enjoying some training classes once a week and although pretends he deosnt know what to do he slipped up in the park the other night when a fellow dog walker called "what's this?" to her dog and Charlie went running over and sat as good as gold! Funny that he doesnt do that when we try! Little monkey - but hey he's 10 and had a terrible trauma of being rehomed so will let him off - for now!