There is a big post-referendum debate in the UK about federalism. I particularly liked this article by Timothy Garton Ash, endorsing a federal UK, a confederal EU and an also federal euro-zone. Federalism, according to a good English friend of mine is a word that has negative connotations in the UK (particularly in England) that create very bad vibes, probably because they've been a proudly independent and strongly unitary state - the UK since 1688 and England since 1066. The word federalism tends to make them think USA, Canada - let alone rule by (and from) Brussels .... "WTO good, EU federal state bad" says my friend.
But there is also a strong British federalist tradition
(which had a strong influence on European federalists like Spinelli) and more and more politicians, like Menzies Campbell, and intellectuals
like Garton Ash or Will Hutton are losing their fear of the F word. As
for Europe, it will probably be something in-between a federation and a
confederation. In the latter, the states keep a lot of their
sovereignty and there is little relationship between the confederal
level and the citizens. In a more integrated Europe (something I think
is desirable) I find a federation more democratic. But there is not one
single federalism, and we should collectively find a unique agreement, one about an institutional architecture
that will be flexible and asymmetric. Until the XV century, there was a lot of diversity of collective organizations, which later disappeared with the consolidation of nations states. But al the local and regional level, many of those diversities survived. For example, in Italy cities are stronger than regions, and in Germany regions or states are stronger than cities. In a more united Europe, there should be room for constrained but real flexibility and innovation below the European level.