I don't know how big the base is....but there is an American sector from what I've been told..
No matter it's size, doesn't sound like it has very much to do with local security if that is so bad there and the Brits are in charge of that sector of Iraq.
Our forces from just south of Baghdad and on north and west to the Syrian border have a very different approach from the Brits.
It is aggressive, works closely with Iraqi forces and has a plan such as to nab Zarqawi and all his ilk. It has a plan to win the people of that area and set up the Iraqi forces to do the same, only even more so because they ARE Iraqi, after all.