Phil L wrote:

* Is it possible to screw entirely new plasterboard over the
sagging plaster, and the hole, and the existing ceiling? This seems
perfectly possible from reading
http://www.diyfaq.org.uk/miscellaneous.html#repairing and similar,
but the problem is that the existing ceiling has stippled plaster.

It doesn't matter if it's stippled or not, plasterboard screws come
in a few sizes and anything less than 3 inches is a POP*

OK, so would I want to screw the new plasterboard directly onto the
stippled ceiling, or use spacers to leave a gap, or try to file off the
stippling somehow before screwing new board down?

Dave