On 08/03/2018 16:44, SteveE wrote:
My 89 y/o mother can no longer reach the switch above the mirror and I
want to change it for a LED pullcord light.

The old light was installed by a bathroom fitter and was not earthed.

This light requires an earth connection but further investigation has
revealed that her upstairs lighting circuit has no earth.

Can I borrow an earth from an accessible ring-circuit in these
circumstances?

If it's a pullcord don't bother with the earth. Put a label on the
switch: No earth.

Bill