The border with Northern Ireland doesn't matter from an economic perspective. What this is really about is the massive proportion of our trade which passes through the UK to the mainland. Trade with the UK, obviously including NI, accounts for 16% of our total trade. Our trade with the mainland (EU excluding UK) accounts for 34% of our total trade. It is the free movement of that which we must protect as a large proportion of it currently moves through Britain.Our corporate tax regime advantage trumps all these factors. If it really does look like coming to the UK throwing the toys out, Leo should concede; think of the brownie points that would give us on the CT thing. It would be the end of Leo domestically of course, won't happen.