"TheScullster" wrote in message ...

Yes I would have googled first, but don't know a suitable key word

I know www.ironmongerydirect.com do them; fairly expensive though.
They are intended for fire safety purposes - they are intumescent,
which means that in the event of a fire they expand (bit like that 'no
more gaps' foam stuff) to fill the hole made by the downlighter to
inhibit the progress of the fire.

David