Obamas
Stansted is the airport where all hijacks are sent to. In that respect the British (and US?) security forces will have outstanding knowledge of it and can thus easily plan for a presidential arrival:and they are meticulous.
I don't know if this is apocryphal, but when either Clinton or Bush jnr dropped in a pub for an 'impromtu' pint with Blair during a visit, the place was cased out for four days before, checked for guns and poisonous beer/food etc.