saying "We are declaring an emergency" must mean something else, apparently.
It doesn't mean anything.
My favourite place for an emergency is LHR.
Once, long ago:
Bas: Mayday x3 Fire stbd engine request priority app.
LHR: Heading 240 clear ILS 27L break x2 LH Go around straight ahead 3000ft call app xxx.
Bas: (Thinks) HTF did he know I was going to declare an emergency?
Respect!