Andy...
In fact what I want to do is reposition my TV aerial which is in the
loft. It has been really hard getting the right position for the aerial
and I need the TV to be there as I adjust its direction and position.

As the TV has no earth then I figured it's ok to run it off one of the
hanging lights in the loft (there are no mains points there). The TV is
a portable and uses about 70W when steady so the current loading should
be ok.

I'm sure that you will be able to tell me why it's not a sensible
suggestion - but what on earth is wrong with a 13amp extension lead? It
would be much safer and much more useful.

David