Brian and Michael also known as Burke and Jerk, real names Kevin Parrott (whos brother Nigel was a member of the Dooleys later in their career) and Michael Coleman.
The original Brian (the one who's actually on the record) is Brian Burke (hence "Burke and Jerk"). Brian left just as the record was becoming a hit, so Kevin Parrott replaced him. Incidentally, Michael "Mick" Coleman also wrote, and Kevin Parrott co-produced, Claire and Friends' immortal hit "It's Horrible Being In Love (When You're Eight An' Half). Triviaaaaah!