Indian currency. These were a continuation ( after postal independence) of the British Postal Agencies in East Arabia GB overprints. As the agencies were originally in one of the Indian "postal circles" they were denominated in Indian currency. I am not sure whether they were actually paid for in Rupees, or whether they were actually sold at the local currency ( if any) and the nP/Rupee was purely for accountancy purposes. Perhaps a former expat worker knows? - there were many UK workers in the Middle East, as there is today.