Hey
I use to work there, so while obviously not an official answer it may help.
You can do an IR course in any JAA state and the UK will add it to your licence.
Since I've left they've created a new application for this - the SRG 1193
http://www.caa.co.uk/docs/33/SRG1193FF.pdf
INCLUSION OF AN INSTRUMENT RATING AEROPLANE IN A JAR–FCL PILOT’S LICENCE –
APPLICATION (FOR IR COURSES
NOT APPROVED BY THE UK CAA)
There's guidance at the bottom showing what you need to supply with it.
• All original Flying Logbooks
• Flying Training Records for the IR training completed
• Actual non-UK Instrument Rating Skills Test Form
• Copy of IR Skill Test JAR Examiner Approval Certificate
• Copy of JAA Simulator Approval Certificate
• Copy of Training Schools JAR Authorisation Certificate
• Payment form SRG\1187
I'm not sure why they need training records, surely a logbook showing you've completed a non UK JAR approved IR course is enough, along with the SRG1193 signed off by the head of training to say you've completed their approved course. I'm not even sure the admin staff there in P LD know what a NDB/VOR or ILS even is, but who am I to argue?
Hope this helps.
VJW