For EITHER a UK or EASA initial IR skill test, familiarisation flying and the test itself must be flown in the relevant airspace - EASA for an EASA IR, UK for UK IR.
I think this only applies to ATOs approved out of theatre. For instance, a US-based ATO training for the EASA licence has to include famil flying and IR test in EASA airspace whereas an EASA-based ATO can conduct the test in non-EASA airspace if it wishes.