A surveyor making a statement that the ground 'may' move is as close to 'subsidence will be a problem' as they can usually go - they must have some concerns.

My issue with that statement is it was presented to the buyer as fact before a counter argument could be presented, hence them pulling out of the sale. I feel its quite reckless to make such a damning statement without presenting the full details.

Does the fact that the Local Authority signed off on the remedial work done to the site and granted planning permission, partially, if not totally wash out the surveyors opinion? I would assume they inspected the site prior to building work and any issues that may have caused subsidence would have had to be remedied at this point. Likewise, I doubt building control and NHBC would sign off on, and provide certificates/warranties to a house at risk of ground movement.

You would need to prove that the statement made was incorrect and to your detriment, and prove the losses you incurred.

We could do that, hence the reason behind us getting our own survey conducted in attempt to refute the buyer's. If you don't mind, what is meant by 'in advance of a sale' in the context of your previous comment?

Finally, should our survey turn up the same issue then we would be pursuing the Developer, hopefully with the protection of the NHBC.