GLASGOW, Nov 1 (Reuters) - Britain is ready to respond in a “proportionate” way if France chooses to carry out the threats it has made in an escalating row over post-Brexit fishing rights, Prime Minister Boris Johnson’s spokesman said on Monday. The spokesman said Britain stood ready to respond in a “calibrated and proportionate” manner if France went ahead with measures that could snarl cross-Channel trade. (Reporting by Elizabeth Piper; editing by Michael Holden)