I did exactly what Nick said but instead of sending me the email with the attachment, they sent me the ordinary confirmation to my iPhone. v( I was too busy to do anything about it there and then but later on, while I was in Cork airport and just about to board my flight to LHR, the email with the attachment popped into my email on the iPad.
That night the wifi in the Premier Inn was so flaky that I couldn't resend it to the iPhone so decided to go the usual route.

So there was I, sitting in the CH having ordered brekkie and what pops into the mailbox on the iPhone? Yup, the Passbook attachment!

)