Mmm... no, I don't actually think GCHQ trust the Plods anywhere near that much (i.e. they are not cleared for relevant SCI; usually not even TS, just C or S!). If they do (and they might, these are just my impressions) I'd be quite surprised.

The NSA definitely work closely, frequently and directly with the FBI, DEA, CIA, and many other US Government agencies, especially since 9/11 and all that "fusion center" business. We know that. They're quite proud about it.

But the old boys from Cheltenham are very conservative indeed, and though they work frequently with The Security Service (MI5) and the Secret Intelligence Service (MI6), I think they rely on the intelligence agencies to do liaison with any law enforcement (notably MI5 with certain branches of the Metropolitan Police) and that only happens in pretty rare cases, nearly all of which are espionage-related or terrorism cases that I'm aware of (drugs are considered a Police problem, not an MI5 problem - we have no DEA analogue).

It's nowhere near as connected as you have over there, and that's for cultural/service-rivalry reasons as well as operational (budgetary? They're not as flush with cash as NSA are) and trust ones.

The Police and their powers under RIPA are more often on their own with that kind of thing. That's why the Government is pushing the whole emergency data retention thing - those powers are more frequently used by law enforcement (but RIPA doesn't really affect GCHQ at all).

I don't think the new "National Crime Agency" has actually changed that setup much, if at all; GCHQ seem to hold them in low regard. Old boys versus new pups, and all that.