Well, I am working on a TL where the French manage their economy better post WW1. That leads to a much stronger France as well as a stronger Spain, Poland, Romania and Yugoslavia (beyond them the economic butterflies get much weaker). The depression is much the same for Britain (though Britain may leave the Gold Standard later, due to France being able to help stabilize Sterling for longer) and world trade is balkanized much as it was OTL. Germany still recovers her place as a great power, but, unlike OTL, it doesn't cause a general war. Instead, Europe settles into a sort of multipolar cold war.
How I see things as going:
India and Egypt are already lost to the British. The Dominions are already slipping away as London repeatedly showed it had a tin ear for their needs. However, without WW2 confirming the lessons of WW1, I wonder just how far the drift might go. The British are likely to be thrown out or withdraw gracelessly from Palestine. What happens to the rest of the Empire I'm less sure of. I do think that the British would still be trying to expand the Empire in the Middle East (they correctly identified oil as being key to their remaining a Great Power), possibly in other oil-rich areas as well. Northern Ireland will become a problem at some point.
I do think that even absent WW2, America will be drawn out of its isolation. American industry was simply too tied into international trade for it not to. That could well mean that the US (as OTL) will compete with the British for the allegiance of the oil rich states in the Middle East. OTL, that competition wasn't very intense due to British weakness. Without WW2, it could look very different.
I reckon British population growth is likely to be lower absent WW2, due to less immigration and the lack of a post-war baby boom.
The economy I'm not sure about. On the one hand, the British economy was close to stagnant between 1918 and 1938, but post war the economy grew quite fast (for Britain), on the other, without WW2 then a whole host of wounds aren't inflicted on British industry (so the army doesn't rob industry of all the skilled manpower, the Sterling zone likely goes strong into the mid 60s, possibly into the mid 80s or even beyond so Britain avoids a detrimental dollarization of her trade, R&D continues along its pre-war trajectory, etc).
Trade isn't disrupted by the war, but on the other hand, without WW2 (and America emerging as premier power afterwards) I am not sure that world trade would liberalize as fast, if at all. The world could continue with high tariff barriers balkanizing trade for some considerable time.
fasquardon