In reality Chris, I am sorry to say you don't have a claim.
In law, either party can pull out at any time before exchange
So that could have been you or them
However, what I would do is write and complain to the Chief Officer. That department will investigate the matter and report back to you.
If they do not uphold your complaint you can then complain to the Local Government Ombudsman.
They offer a free, independent service and can examine your complaint for free at: www.lgo.org.uk
Those are the steps to take if I were you.
Beyond that, sadly they are entitled to pull out.
I am sorry if this is not necessarily the answer you want, nor the one I want to give you, but I have a duty to be honest.
Can I clarify anything for you about this today please?