EASA would not tell you that:
YouŽll find the basic regulation within
Part-FCL (Article 8 on page 4 and Annex III, p169 - 172).
But it only says, that a foreign license "...may be validated by the competent authority of a Member State"
So, under the rules of Annex III, the CAA in UK had to specify, if and how they validate and/or convert FAA licenses.
You will have to ask the CAA how they did it.
Have fun
Thracian