An effective border control controls permission at the point of entry.
Which powers that we have which we dont exercise could stop EU people gaining entry?
My point is, the UK government has decided it does NOT want to stop EU people gaining entry, post-Brexit. Anyone from the EU will be free to come and go as they please - as long as they don't work or claim social security. It's a slightly bizarre scenario, as (a) EU nationals are currently net contributors to the UK economy (ie, they pay more in taxes than they claim in benefits), and (b) we need MORE immigration not less - certainly in the south of the UK - there simply aren't enough people to do the jobs required. People are worried that EU citizens come to UK and "sponge off the state" - the UK government could put a stop to that immediately (if it were true). Funnily enough, it chooses not to.