You can claim a maximum of 30 hours towards the 40 hours course if you have flown under IFR and IMC conditions under the privileges of an EIR, ICAO IR or IMC/IR(R).
The base requirement is that you will require a minimum of 40 hrs IFR experience (for CB-IR on SEP) prior to being permitted to take the Initial IR Test can be made up of credits that you can claim for prior experience or for prior training up to a maximum of 15 hours of prior training. (Which could be the training you did for your IMCR) and or up to 20 hours of your own prior IFR experience that you might have gained as captain on flights after you had obtained you’re IMCR/IRR.
Further Guidance on specific routes to gaining a CBIR can be found on the UK CAA website.