Steve Glover, who has tended bar in Ireland, says that the layered Black and Tan is an American affectation that they were happy to do for extra money :-). Otherwise, both beers (they used Smithwicks and Guinness) were simply poured in the same glass fully mixed.(From the Black and Tan FAQ link above).

Ah, that explains it- never heard of it being layered. Very popular drink when I was in Liverpool, and it always got mixed!

Good luck, Tom- I think it would have to be draught Guinness to work, but enjoy every pint that doesn't work too!

Noreen