Only if it's a UK-issued JAR-FCL ATPL and an IMC Rating had been included (paperwork and fee exercise only):
"The holder of a JAR-FCL professional aeroplane licence with a valid multi-pilot IR(A) is not automatically entitled to fly using the privileges of an IMC Rating in single-pilot aeroplanes. They will be required to obtain a separate IMC Rating endorsement on the basis of their most recent multi pilot IR proficiency check or skill test. In this case, the IMC Rating will be valid for a period of 25 months from the date of the IR(A) skill test and will not need to be revalidated if the IR remains valid. If the IR(A) lapses an IMC revalidation flight test is required."
It's all because the CAA cocked up the 'included IMC privileges' of the former UK (non-JAR-FCL) CPL and ATPL when the JAR-FCL scheme was inflicted upon us!