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So the UK has a process called the Reciprocal Enforcement of Maintenance Orders, which the US is part of. You will need to apply for your alimony order to be enforced in the country where the payer resides (the UK). Note though that Alabama, Mississippi, South Carolina, and DC are excluded from this process and therefore alimony orders from those states cannot be enforced even when properly presented in the UK.
You may want to contact the "International Family Law Group" that practices in the UK. They may be able to help you enforce your alimony order overseas. Their web-address is: http://www.iflg.uk.com/services/finances/enforcement-of-foreign-financial-orders