On 08/12/2016 13:05, Mike Clarke wrote:

Depends on how heavy it is.

I will try first if space allows to fit to joists, otherwise a batten to
the topside of plasterboard.

Bog standard light fitting nothing elaborate.

If you're concerned about loading the plasterboard and have enough
access to reach the space above but not enough headroom to screw in a
noggin you could try fabricating a loose noggin the same height as the
joists with an extra and longer piece of timber screwed on top of it
which will rest on top of the joists. When you screw the light fitting
through the plasterboard to the noggin any loads should be carried on
the top of the adjoining joists. It might be a two person job to get the
first screw started, one in the loft to hold the noggin down and another
below to drive in the screw.

Weight, in total with lightbulb about 300 grams.

Thanks again for all the suggestions it will now be done one way or the
other.