“70,000 Spanish in the UK compared to about 400,000 UK in spain “
Of course a more apposite conclusion to be drawn from the table provided would be 674,000 UK citizens living in the other countries mentioned and 1.16m people of those nations living in the UK. The point being, of course, that Spain would not be the only nation affected.
However, incredible as it may seem, people from the UK did up sticks and move to other countries and people from elsewhere settled here long before the EU allowed unfettered movement. Of course there will be extra paperwork, but since that will fall on the people moving out it would be a small price to pay to regain control over those whom we let in and who will be living amongst those who remain.