The Quietus has a brilliant interview with Shane McGowan; one of the highlights is McGown revealing his unexpected collaborators. The dead:
"I actually see people dictating to me behind me through… they call it the third eye, but the Japs reckon you've got at least eight, apart from the two here. I've seen ghosts behind me in period costume dictating songs on a couple of occasions. 'A Rainy Night In Soho' was automatic writing. I had no idea what it was about. I had a vague idea by the time I got to the fourth verse but until then I hadn't got a clue what was going on."("The Japs"? Really, Shane?)
It's not entirely unlikely that ghosts would want to work with Shane - if you died years ago, had no body to talk of and some people find your continued existence a befuddling scientific impossibility, wouldn't you look for someone similar to work with?