Alien in a pub

An alien walks into a busy pub and asks for a pint. Landlord says, "sorry don't serve aliens."

Alien says, "I'll buy you one?"

"Nope, dont serve aliens."

"I'll buy every one in here a drink?"

"Nope don't serve aliens."

"I'll buy all the drinks all night for everyone?"

The landlord agrees.

A few hours later the landlord says, "Right that's £3,450 please"

Alien says,

Spoiler:

"you got change for a zonk?"