Irishman and the knocking shop

An Irishman goes out on the town one night and gets well and truly drunk. At the end of the evening, he fancies a spot of how's-your-father so makes his way to the local knocking shop.

Unfortunately, having spent so much money on booze, he only has £5 left. Nevertheless he knocks on the door and the Madam opens up to hear him ask:

"What can I get for a fiver?"

"Five quid! Five flamin' quid! You've got to be joking - now off and go play with yourself" she laughingly replies.

Disappointed, the Irishman turns and trudges off.

Five minutes later, he returns and again knocks on the door.

"What the do you want now?" she asks impatiently

Spoiler:

"Who do I pay?"