I have found that, by activating a scenery layer "UK2000 AFCAD2 files
High Level", the apparent misalignment at Bruntingthorpe is partly
fixed. There is no longer any "double-vision" of UK2000 scenery and MS
default - only UK2000 is visible, and locating to the active runway puts
me in the correct place, not in the middle of a field. BUT ...
Examining the picture in FSNav, I see that it still displays the default runway and, consequently, my aircraft appears north of this, and none of the UK2000 scenery taxiways appear in FSNav.
Two steps forward and one back, it would appear. Progress though ...