Sorry if I was not clear enough.
In the case you have explained it can. If Germany has taken any UK territory(Canada or Africa), then the US will collect the income if it retakes it.
As soon as London is liberated, the former UK territories the US recaptured from the Germans will return to the UK.
Blitzing question
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As Japan I have just taken over China from Kwangtung. Can I now blitz through my new China territory with the stack of unused tanks I have in reserve in Kwangtung and take over Sinkiang or do I have to wait a turn?
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You have to wait a turn.
Blitzing is a combat move, where you blitz through an unoccupied territory and take it, either to engage in combat in an adjecent territory or to move (or return) to an adjecent friendly territory.
In your case your combat movement phase has ended, since you have already resolved combat in China. You can not take Sinkiang in this turn then, since it would be a combat move.