I´m not certain, how US passport holders are treated. For all others: Well, if you move to UK or EU from outside you will be assigned to a european entity ( UK for UK residents, Ireland, Luxembourg or Hungary for other european residencies - IB`s decision). Under the new EU and ESMA rules there is only ONE residency, as taxwise physical residency is assumed where your wife/family resides, if any doubts remain beyond the 183 days rule.