Thanks to everybody for the replies, your help is very much appreciated.
To answer a few questions:
- The party wall award didn't cover the shared chimney. It became an issue because the neighbour complained about our builders' proposed approach to dealing with a step-down between the two flat roofs (our property is slightly higher than the neighbour's). In the end the surveyors recommended raising the parapet wall between the two properties, which made it necessary to raise the height of the chimney stack (and we decided to cap it off in the process).
- The scaffolding was taken down, so new work to the roof now comes with an access issue.
I've attached a couple of photos. The original mortar cracked in the hot weather last year and was subsequently filled in.
It's helpful to see examples of good practice, thanks for sharing the link above TonyT. Nobody (builder, neighbour or surveyors) has shared any reference material so it's hard to figure out what good practice looks like. We want to do it right, even if it costs extra, but hard to work out what 'right' looks like.
I think we probably need to do the coping. Hard to find a roofer or bricklayer interested in the job, but that's a whole other story...
Thanks again!