New Delhi, Oct. 23 -- Indian investigators are examining whether Diageo and Pernod Ricard wrongly claimed a lower import duty on bulk Scotch concentrates after the India-UK free trade agreement took effect, according to details shared with the companies and a letter from their trade body.

The Directorate of Revenue Intelligence searched the offices of both firms this month and questioned executives as part of the probe. Authorities have privately told the companies that the reduced 75% tariff does not cover bulk Scotch concentrates. Those shipments, they say, must be classified under a heading that still carries the full 150% duty.

The case centres on how the companies import bulk concentrates from Britain and blend them in India to pro...