Guy Snape wrote:
Is there a glue suitable for sticking the spout back on to a teapot?
Obviously it would need to be resistant to heat and water, and not
dissolve into the tea and poison us.

I simply would not do this. The danger of hot (near-boiling) liquid
spewing out over people (or just me!) when the spout fell off would not
be fun.

And, depending on the damage that caused it to fall off in the first
place, you might find it still unusable.

--
Rod