You need to pass the JAR State of Licence Issue requirements.
Downloads LASORS section A
http://www.caa.co.uk/lasors
Look at A8.
An applicant may only apply to change the state of
licence issue of a JAR-FCL licence provided that
employment or normal residency is established in that
state. Normal residency means the place where a
person usually lives for at least 185 days in each
calendar year because of personal and occupational
ties or, in the case of a person with no occupational ties,
because of personal ties which can show close links
between that person and the place where she or he is
living.(JAR-FCL 1.070/2.070 refers).