I’m just in favour of decentralisation, every time power has been centralised in Europe it has ended badly.

I want to express my thoughts on this point. I believe that two things are true at the same time:

1. Cooperation beats competition since competition wastes resources by hindering each other when those could have been better invested in reaching the shared goal.
2. Representative systems get less efficient and more prone to corruption the bigger they get.

Concerning European this imho boils down to two contrary tendencies: The bigger the EU and its bureaucracy gets the less efficient it works while at the same time the efficiency of the EU economy is increasing through ever deeper cooperation and standardization.

Following this line of thought, the question of whether the EU benefits or harms its citizens is largely decided by the ratio of additional costs due to bureaucracy to benefits due to cooperation. Since the advantages of cooperation, especially within the single market, are immense (and are becoming increasingly important in a world where the major powers are increasingly hostile to European states), I tend to view the EU positively, even if centralized administration can create new problems. After all, what would be the alternative? European nation states have worked against each other and waged war for centuries. Now that the European colonial empires have collapsed and lost a great deal of influence, I find it highly questionable that this model would be promising in today's world.