> I'm not familiar with the situation of New Zealand with respect to Australia (its neighbours). But the problem in the EU, is that there are a few countries (Ireland and the Netherlands inside the Union, and Switzerland which is right next door and enjoys many advantages and no constraints) which charge way less tax than the "central" EU countries. So companies have a tendency to set up their HQs in those countries.

Speaking as an Irish person, this is definitely true and tax is a big reason for a lot of the multinationals we have here.

However, also note that the Irish people have one the highest debt per capita, basically incurred to pay off debts to EU/UK banks during the financial crisis. If you mutualise debt, and do the capital markets union then you could 100% fix this (but the political will definitely isn't there for that).