Nigel Farage walks into a bar, and up to the landlord, who is serving.
Nigel : Pint of best bitter please?
Landlord: That'll be three pounds twenty.
Money & beer change hands and Nigel moves aside to allow room for more customers.

Jeremy Corbyn walks in, and approaches the landlord:
Jeremy: I'll have a pint please?
Landlord: Five pound please?
Jeremy pays up, sees the money go in the till and is handed a pint of water.

Jeremy ponders this, and spots Nigel drinking a good pint. He goes over.
J C: Hi, Nigel, what are you drinking?
N F: That's kind of you, but I've already got my pint of best bitter.

Jeremy beckons the landlord to try again.
J C: A pint of best bitter please?
L: Five pounds please?
Jeremy pays up, and receives his beer (the head may be a little large, but he doesn't complain)

A couple of minutes later Nigel finishes his pint and beckons the landlord.
Nigel : Pint of best bitter please?
Landlord: That'll be three pounds twenty.
Money & beer change hands.

Jeremy has watched this exchange and approaches the landlord.
J C: Why have you just charged Nigel three-twenty when you charged me five pounds?
Landlord: He wouldn't have paid it.