> Among expat Britons in Spain who voted for Brexit, was this a common attitude that they would be allowed to stay? Or were they told they would be allowed to keep residency rights?

https://ig.ft.com/sites/expats-on-brexit/ has some pre-referendum views of British emigrants. One says "I want practical facts. The Government and Brexit campaigners have been silent on what will happen to Britons abroad if we leave.".