1. For the initial isue of a UK IMC Rating, note that:
An applicant who has held an ICAO or military green
Instrument Rating or a UK professional pilot licence aeroplanes
in the 2 years preceding the date of application for the IMC Rating will be exempt from taking the initial IMC Flight Test and written examination.
So, just get fill out the SRG 1125 stating your exemption and attaching logbook proof of your FAA IR, together with payment of £70 to the CAA. Download the form from this site:
http://www.caa.co.uk/publications/pu...e=formcat&id=2
2. To re-validate or renew an existing IMC Rating, note that:
An IMC rating may be revalidated/renewed for a further period by the CAA, on the basis of the most recent Non-JAA IR(A) flight test. A fee is payable if the C of T is signed up by the CAA.
No test needed and (probably) nothing to pay in this latter case if your Examiner merely needs to check your log book for evidence of your FAA IR validity before signing the National Rating - Certificate of Revalidation page in your licence.