Loaded Question

We all know that we have a prison camp for captured terrorists at Guantanamo, and maintain detention facilities at other locations worldwide.  These people come from a plethora of countries, a lot of whom we have at least semi-friendly relations with.

What do we do if the governments of those countries, when they learn that we have captured their citizens and are detaining them in a state that's not really criminal, but not POW, demands access to them, or even demands that a representative from their diplomatic corps be present when that person is questioned?

Let's change the way we look at this.  Let's say that a British subject is in our country on a work visa, and is arrested on suspicion of rape and murder.  Since those crimes are pretty heinous, and he's a flight risk to return to Great Britain, we hold him without bail.  Can the British ambassador demand access to him and provide counsel for any interrogation and and have a reasonable expectation that we do as asked?  We could demand the same thing for one of our citizens, so would we turn down their request?

What if that British subject was arrested for espionage for a third country, say China?  Would our response to the Brits be any different?

Now, let's say this British subject was captured in Afghanistan.  He's suspected of being a member of Al Qaeda, and is being interrogated by our intelligence services.  How do we react if the British ambassador in Washington demands that a British diplomat be allowed access to him at Guantanamo and be present during any interrogation?  Update:  A quick Google search shows that this has happened in the past, but it looks like a case by case kind of thing, not a blanket notification to home countries and almost automatic access to a citizen by diplomats.

What if the detainee is from Saudi Arabia, or Iraq, or Russia?  Or say he was a German citizen, a country that might not look as favorably at our interrogation techniques as some of our other allies? We can expect a German diplomat to object strenuously to our applying harsh interrogation techniques to one of his citizens.

I know that we need to interrogate these prisoners and keep them away from the outside world as much as possible.  Sometimes our interrogation methods, while legal and justified, can go beyond simple question and answer sessions.  I'm a former intelligence soldier; I know how important the information gained in these interrogations can be.  But the implications for international relations and how our own citizens are treated if arrested or captured are huge.  I'm interested to know if anyone has any insight on how this is handled, and to hear y'all's opinions on whether or not we should allow foreign diplomats to access their citizens while they are in our custody.