The proper analogy would be refusing to give a combination for a safe, which you can probably do, its not such an issue because they can break the safe open.

Exactly.

I think there is actually precedent (in the US) here, but I can't find the reference. I will keep looking.

I'm pretty sure that you can't refuse a search warrant.

Edit: see fatdog's comment for why.

No, you can't.

The 5th amendment right to avoid self-incrimination only extends to testimony. A search warrant can compel you to furnish the contents of a safe (as property, it is governed by the 4th amendment -- due process is all that is required, and in this case, the process of getting a search warrant is all that the Constitution requires).

im not sure but I think that was his point (only using the reverse argument)