But that's not at all concrete though, is it?
The future is not concrete. You could die tomorrow, I could rop dead in the next 10 minures. Life is about uncertainty - we deal with it.
It must be possible to imagine some way in which border controls will change, in order that border control agents can be better equipped to secure the borders in a way that they are not able to do now.
Blame Cameron. He knows the answer to that one but is with-holding it from you.
Cameron could come out this evening and say 'If we leave the EU will still allow 15 yer old French children (or any other category) to travel to the UK on their ID card/passport.
He won't because that would diminish his Project Fear.
Say you're a border control agent. You have in front of you my teenager, carrying a French passport, who looks (like most kids round here do in summer) more than a little bit tanned. His passport says he's 15 and French. How are you going to decide that he is what he claims to be, and isn't a 20-something Syrian travelling on false papers? And most importantly, how will that be different to what happens now?
As I said before - Cameron knows the answer because post-Brexit he tells us he will still be running the country, so the decision on how the border is controlled is his.
Visas would help solve this problem of course
A lot of countries think so - many countries don't.