What if, through a series of accords, the pound was accepted as the currency that all cash is compared to instead of the USD?
Would that be detrimental to the States? How much will europe benefit? Will this butterfly away the EU? If there is a EU, will Britain join?
I really think you need a pre-1900 POD for this.
The British Empire has to be economically stronger than the US empire.
I suppose that IN THEORY some alt-version of the EU might use a currency based on the British pound, but even so....
Hmmm....
In 1945, the USSR collapses (why? Stalin assassinated, massive internal power struggle between Beria, Molotov and Zhukov? ???)
Nazis defeated. US pulls out of Europe in, say '47 or '48. Germany is still in ruins, France has a period of hyperinflation, British pound is in sad shape - but best of a sorry lot. European nations (initially UK, France, the Benelux nations, Denmark and Norway) form a free-trade/self-help plan to pull themselves up by their bootstraps (no Marshall Plan). Associate membership to Poland, Czechoslovakia, Hungary and Austria.
When US pulls out, Britain and France repudiate their war-debt to the US, making their economies healthier and the US's worse.
Umm.... Sounds rather ASB to me, but it's the best I can think of.