So I emailed the CAA to seek further clarity on the matter. And this is what I have in writing from them. Seems to concur with the general consensus on this thread.
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Thank you for your email regarding the difference between and modular IR and a CB-IR. I confirm both are an instrument rating gained through a different training route. Please refer to CAP 804, section 4, Part L page 34 -38. In some instances a CB remark will be annotated against the Instrument rating as a remark. This is in instances such as where the pilot has elected to only take CB IR theoretical knowledge examinations or elected to be orally assessed as part of the IR skills test.
http://publicapps.caa.co.uk/docs/33/...searchable.pdf
All information provided is based on the requirements and regulation as at the date of this email (11.01.2016)
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Just in case anyone here is interested! :-)
Also... Did anyone know about electing to be "orally assessed" as an alternative to presumably the CB-IR theoretical examination?
Sounds interesting....!