This has been asked, maybe, 20 times on here? Most recently, 4 days ago:
http://www.pprune.org/private-flying/523081-ir-r.html
You can add an IMC rating, as an "IR(restricted)" to an EASA Part-FCL licence before April 2014. The IR (r) is identical in all but name to an IMC rating.
After that date, unless something changes (which various people are hopeful about), you can get a separate UK PPL which you can add an IMC rating to. However, the use of this UK PPL would be restricted to Non-EASA aircraft (such as SA Bulldogs, but not PA28s or Cessnas 152s).
HTH
RR