I think that if we can establish a free trade area which includes the dominions then we'll have broken the barriers of protectionism and the rest should follow logically in time. Do not forget that the Dominions do want further immigration - perhaps we could focus on the white dominions first (or rather avoid India and Pakistan) in order to reduce fears of the "wrong kind" of immigration to the Dominions.
This is why it is so important to get the Dominions onside. If we can get a minimum of Canada, Australia and New Zealand on board, perhaps India and the Pakistans too if we're lucky, then the rest of the Commonwealth will fall into place.
However do you think it is possibru to be part of both the CEA and EEC?
In real life Eden spoke of something called the "three circles" of British foreign policy: The Atlantic Alliance with America, (or NATO, if you will) the Commonwealth, and Europe (or the nascent Common Market, if you will) being those three circles. Picture a venn diagram if you will, with Britain in the centre of those three circles, and you have your average One Nation Tory's view on foreign policy.
Bah, you are advocating neoimperialism!
All provinces of the Empire are equal and deserve equal rights and presentation in the parliament of the commonwealth!
Humans are all equal in front of the law, whether they live in the jungles of Sokoto or on the isles of Britain!
When did it stop being an issue?
Depend if it is possible. Depend if NATO and USA want UK to have their own bloc. At the same time it depend if EEC and France would like UK to have it's own market too.
Honestly, America would be totally cool with the Commonwealth Union provided we and it remain anti-communist. Hell, America would do just about anything to prop up such a venture if it meant "outsourcing" the fight against Communism to Britain, and keeping us "East of Suez" so to speak. France of course, is a totally different matter.
Explain why they were so uncool with the Nordic countries forming an alliance then. A Commonwealth alliance would be much stronger.