Railway worker

A railway work is lying on the floor in a station clutching his guts. He’s rolling about in terrible pain and groaning, “Are you alright?” asks a passenger.
“O Arrh, I’ll be OK in a few minutes,” says the worker.
“What’s wrong?” asks the passenger.
“Well,” says the worker, “I’m busting for a shit, but I don’t start work for another 10 minutes.”