Dave3dg: us brits are very welcome on here, and all the engine bits are virtually the same, bar items related to emissions many!!
the N18 valve is the one that controls the EGR valve, I have had the seals damage and allow uncontrolled vacuum to the EGR controller
2 ways I know to test,
1: swap the valve with the one that controls the turbo (n75) and you should notice a difference on start up
2: undo the pipe from the exhaust to the EGR valve, and block it with either metal plate or even some cardboard (not to be driven on!)