George wrote:
"BigWallop" wrote in message

Expandite foam from the DIY Stores. It's commonly used to fill gaps
around windows and doors, but it is also quite a good insulator.
Shake the can really well before using it and keep shaking it
between uses. Be gentle with it, as it blows up to nearly three
times its liquid state when curing.

Cheers. Is it possible to shape it (with a scraper for example) to
the general shape of what's already there or will it look like a
growth on top? :-)

You can cut and shape it with a sharp breadknife.
Or alternatively, if you get the amount just right, cover with a sheet of
tough polythene, taped down well.
This will give you a similar finish to what is on there now,
but as Big Wallop says, it expands to almost three times the size, so go
easy!