Who underestimated Japanese capability

Why is it said that Britain underestimated the Japanese before the Pacific War?

Much of the error lies with Churchill and other politicians, arguing that British intelligence and naval officers repeatedly warned about Japan and requested carrier support.

Churchill's postwar narrative shifted blame away from decisions he helped make. Contemporary intelligence and naval papers, in his account, show sustained concern about Japan and warnings that a deployment without a carrier was unsound. Experienced troops and equipment were diverted elsewhere, while the remaining command structure lacked preparation and integration. The watch point therefore distinguishes institutional knowledge from whether political leaders acted on it.