In message , Christian
McArdle writes
ISTR that it was illegal to make any structural modifications to a party
wall without consent of the other party

I don't think the Party Wall Act requires consent. It is simply a method of
appointing surveyors to look after the interests of the other party. It does
not provide any method for the other party to prevent works, just to ensure
they are done in a structurally sound manner. There are no prescribed
enforcement procedures in the act, either, so it is a bit of a paper tiger,
although you may find the County Court manages to force the neighbours to
make repairs.

Are there are reasons you believe the chimney to not be supported, or are
you just worried in case it is not?

I know it's not supported

--
geoff