Unless the product has been certified for use with classified information, that's not much of an assurance. The government has its own internally-developed tools -- which presumably it has confidence in (SIPRNet, etc.) -- for protecting information that it deems sensitive. The NSA might well decide that subverting a commercial tool is worth the risk of compromising something that's used by the government, but only in relatively trivial ways.

I don't know enough to impugn Zimmerman et al, but I don't think "it's used by the government!" is necessarily a great seal of approval, unless it's a formal certification (e.g. NSA Type 1 listing) saying that it can be used to protect classified information. And I'm not aware of any COTS software products that are on the Type 1 list; the NSA only approves particular hardware implementations (at least that I've seen, though I'm happy to be corrected although I'd be surprised).

On the other hand it's not working for me unless I use a proxy, so I assume BT are doing something to prevent me reaching it.

Strictly speaking a visa is a document that helps you present yourself to an immigration officer at the border. There's a presumption that he/she will let you cross the border, but no entitlement.

i dunno, throwing in a few deportees in the other direction might help bring about a sense of proportion about the merits of copyright law uber alles.

This exists, it's called the SIPRnet. You can only access it from secure workstations in secure facilities, and in theory all the network hardware is also secure, etc., etc.

AFAIK, the only recent SIPRnet compromise was Bradley Manning, and that was more of a social exploit than a technical one.