There has certainly been talk of CAA PPL holders having to undergo additional training in radio nav before converting CAA to EASA licenses, (since JAR regs required such training and CAA licenses did not.)
And conversion of a UK PPL to a JAR-FCL PPL has always required the applicant to "demonstrate the use of radio navigation aids".
"Demonstration of the use of radio navigation aids should be to the satisfaction of a Chief Flying Instructor. Successful demonstration should be certified by the CFI in the applicant’s personal flying logbook" [LASORS]