The message
from "JoeJoe" contains these words:

Problem is that the radiators seem to be getting very cold very quickly as
soon as the boiler is switched off. My suspicion is that the cause could be
because some of the pipes (copper) hat feed the downstairs radiators
are not
insulated.

As others have said, it'll only really matter if the pump is still
running once the boiler's off. I'd lag the pipes in the cold space
anyway, but radiators do cool down quickly - that's what they're for!

--
Skipweasel
Pay no attention to that man behind the curtain.