Re: borders to be regularised or smoothed out by mutual agreement
That turns out not to be the case; look at http://ukandeu.ac.uk/explainers/is-the-uk-marginalised-in-the-eu-2/ and note "The UK government is closer to final EU policy outcomes than are most other EU governments. This is also true for policy issues the UK government is particularly concerned about.". That's an academic way of saying that the Brits usually get what they want.