Thanks for the replies, this problem is now all that is standing in the way of an MoT.

A bit of progress, turns out one of the white relays in the fuse box was duff. I now have a working near-side headlamp but not off-side. This kind of makes sense as the nearside units earth path is straight to earth whereas the off-sides earth path goes via another 5 pin relay according to the diagram in the Haynes manual.

As I cannot find a 5 pin relay in the fuse box I am hoping that this is the blue relay mentioned under the dashboard.

Wouldn't it be nice if Haynes identified the physical location of the relays in their books. Or is that too much to ask?