Professor Siobhán Mullally:

Yes, but we still have a common travel area. If the UK were to opt out of free movement laws and were to be outside of that, apart from Schengen, other free movement protections would not apply, so we would require significantly more policing than we currently have. That would be quite difficult in practice as well as legally.

The final point relates to a comment that was made as to whether the benefits of free movement could be retained. Again, this goes to whether it would be possible to negotiate a series of bilateral agreements or a position such as would be available as a member state of the EEA. As I mentioned, that is very unlikely given that much of the debate has been around limiting free movement. Giving that type of concession is unlikely either to meet the needs or desires of those proposing an opt-out for the UK or those seeking to leave the EU entirely.