Could you explain how the dismantling of INTERNAL borders allows access for outsiders?
Suppose the UK once had internal borders between Britain, Ireland, Scotland and Wales.
When it became the UK, and there was no longer any internal borders, the common borders between the previously separate countries would no longer require policing.
One would expect that the combined resources of the four countries could now be allocated to the most permeable part of the whole external border.
So how could that faciitate foreigners coming into the UK?
If my logic is faulty, please explain how your logic is better.