See CAP 804 Part 1 Section 5 Part E Page 1 dated 30 Jan 2013:
An IMCR first obtained prior to 8th April 2014 can be added in the form of an EASA Instrument Rating with restrictions (IR(R)) to a UK-issued Part-FCL licence at any time in the future, including after 8th April 2014. IMCRs first obtained after 8th April 2014 cannot be added to Part-FCL licences. IMCRs obtained after 8th April 2014 may continue to be added to UK national (non-Part-FCL) licences only.
This is the revised wording we at AOPA UK asked them to include.