Officers investigated powder said to have been sent to the Lib Dem leader's office.
The transport interchange has been evacuated.
Passengers panicked after delays disembarking planes and airport evacuation – but suspect items found in luggage turn out to be replica firearms.
A large area of the city centre has been cleared by police.
Counter-terror police have circulated images to mail sorting offices and transport workers
It is not known if the incidents are linked.
'Mainstream Media must clean up its act, FAST!'
At least six people have been targeted.
Just a normal Tuesday.