Such a Union could easily afford to be leftist, because there are no weaker members.
I looked further at this and its quite incredible how similar the Northern nations are to one another.

Economic Freedom Index: (EU rank / nation / global rank)
1 Luxembourg 3
2 Estonia 4
3 Ireland =5
4 United Kingdom 7
5 Denmark =8
6 Sweden 14
7 Finland 15

Corruption Perceptions Index : (EU rank / nation / global rank)
1 Finland 1
2 Denmark =3
3 Sweden 6
4 Netherlands 10
5 United Kingdom 11

Human Development Index : (EU rank / nation / global rank)
1 Sweden 2
2 Netherlands 5
3 Belgium 6
4 Ireland 10
5 United Kingdom 12
6 Finland 13
7 Austria 14
8 Luxembourg 15
9 France 16
10 Denmark 17