As crazy as it sounds, he may have an angle. Britains have been so dihimmi-tized that I think they allow islamic polygamy in some instances.
His case is certainly much stronger if Islamic polygamy has been allowed; however, I don’t know if recognition of polygamous marriage extends beyond recognition of marriages conducted in countries (usually Islamic) in which they are legal. Because FLDS marriages are not recognised (’recognized’ in the US) in either Canada or the US, the usual diplomatic acceptance of such things does not apply to FLDS polygamy.