Question Author
Thanks all for your input.
As usual in these cases there are possible complications.
The new owners of the site are doing nothing to the site because they want to clear it of residents, so they can redevelop it. They are not a nice family, and have been known to make veiled threats to the residents to scare them into selling - I'm sure you're getting the picture.
We run a business next door (a boarding cattery) and can't afford to p**s them off in case of retaliation which could adversly affect our business, so we are treading carefully.
All very tricky.
The cost of repairing the wall would be a few hundred quid, so we could have it done ourselves, but why should we pay for their repairs just because they're being bloody minded?
The local council are aware of happenings at the site, maybe we could get them to issue a notice to effect the repairs?