I have to agree that it's sometimes easier to remove the sink.
Much the same as any pillar tap,Fred. If you don't remove the sink, then you'll need either tap spanners or a box spanner to get up there........... or a basin wrench......
http://www.screwfix.c...fh_search=tap+spanner
Don't worry about metric vs imperial. The backnuts will be imperial 1/2-inch.
Conventional mixer and pillar taps still tend to be 1/2" today.