Where does the large double rotor helicopter that flies over central london come from?

Question

Every couple of days a double rotor helicopter flies over my workplace near London Bridge. Sometimes it is on it's own, sometimes it has another helicopter with it.

Does anyone know where this comes from and what it is doing?

Answer 1

It flies between the MI6 building and the MI9 building

As for what it does and who it takes, That is a secret !

Answer 2

Probably a Chinook from Odiham, routine stuff in and out of Woolwich Barracks. They follow the Thames or sometimes the big parks, for safety reasons in case they come down.

Answer 3

As Bardic says, it'll be a RAF Chinook from Odiham in Hants.