Ah thank you keberoxu for that. The video (on Youtube) seems to show the St Patrick's Day processions etc in New York, and there is indeed a lot of Irish stuff in it.
But 'pack it oop pack it in' sounds so like Peter Kay, or someone else who cooms from oop North.
I'd never heard of House of Pain.
I really like the advert now,and turn the sound up (or should I say 'oop'?) when it comes on!