Re: This is based on unwarranted assumptions
You are assuming that Teresa May would like to keep UK in the same conventions.
I'm pretty sure that derogating from international obligations that have been enshrined in UK law through an act of parliament requires assent from parliament, rather than unilateral action from the 'prime minister' (a figurehead with no real legal standing beyond being the leader of a single political party within the commons, if you read your history books), even through 'royal prerogative'.
If only we had some sort of legal test case to press home this point...