The message
from Kay contains these words:
In article , Jaques
d'Alltrades writes

You could block the hole in the mortar with something like plasticene
the evening before work is to begin. If they don't emerge from the
chimneypot in the morning, that should fix the problem, and any worries
about the unlikely possibility of igniting the nest.

And then let them out again when the work was over? Do you think they'd
be OK? (Apart from cross, that is)

They'd probably be OK - depending on how many bees and how much
available air there was. You could find some gauze or net curtain and
stick it over the hole using Blu-Tak or some sort of glue.

Attach firmly a long string, and when the job is done, pull it off from
a distance...

--
Rusty
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