Performance restricted warning Discovery 4 - water in fuel

[alfabeat]

Had this warning pop up a few times recently, although no actual restriction in performance. Got my codes read by a mate, and it comes up with the fault being water in fuel related. A quick google reveals this is most likely a fault in the plastic housing which the fuel filter attaches to.

So I get a new housing and filter from the local LR specialist (£100 odd). What a pig of a job to replace. There is just not enough space to get the old housing out and the new one in.

Any tips from the experts on here?