So, I put an offer on a house which was accepted. At the time, the vendor claimed all the paperwork was in place for a loft extension, but it turned out they didn't after we had the conveyancers exchange paperwork. To proceed, we agreed to have a structural engineer investigate and we'd share the cost. The vendor have now decided they don't want to do that because of the disruption (of revealing the structure of the property), and told us to sod off.
I don't feel I'm being unreasonable, but the estate agent and vendor are claiming I am being silly, and have put the property back on the market.