One is measured in pounds. The other is measured in pounds. Seems pretty comparable.
If you're being deliberately stupid you could pretend it's a comparison between pounds and pounds per year, but everyone who is at least minimally literate in the subject understands that "GDP" here means "the amount of value produced in a year".
If you're being deliberately stupid you could pretend it's a comparison between pounds and pounds per year, but everyone who is at least minimally literate in the subject understands that "GDP" here means "the amount of value produced in a year".