Janet and Spider: thank you very much for your fulsome advice!

The holly in question has been where it is for quite a few years. I'm
not moving it very far -- just six feet further into the shade, and my
concern was/is that it will miss out on direct sun for probably nine
instead of six months of the year. The new site is very damp, and it's
not directly under the north side of the house -- just in the shade of
it.

I think I'll give it a go, and (I hope I remember!) I'll report back in
a few months time.

The reason for the transplant is that the area I'm moving it to is
pretty useless (shade all year): it will look better with a nice glossy
holly there (especially if it retains its variegation). And it will
free up a sizeable area, in a sunnier part of the garden, for my wife's
flower growing :-)

Thanks
John