JimmyH: In a past life I had a secondment involving working with sensitive information, for which I had to hold a security clearance. We were supplied with laptops with encryption by the employer. It was a dismissable offence for me to disclose the information in question, or even discuss it with someone who didn't have a clearance. It was also a dismissable offence to give anyone my password. Certainly my market value would have been severely damaged.
I am pretty sure that a run of the mill Customs officer doesn't hold such a security clearance.
Therefore, I think I would have been in a world of hurt if I had handed over the password to anyone.
(but no, put the tinfoil hats away, the job was nothing to do with any spook agency).
I hope someone is putting these kind of questions in a submission...