From Dr Ken Shadlen.

Sir, Alan Beattie ("Trading ritual and reality", September 19) observes that many bilateral and regional trade agreements have minimal effect on trade flows, and concludes that these agreements are insignificant. He is correct that many of these agreements are signed between countries that are already trade partners, so the additional trade is often minor and insignificant as a share of global trade. One could counter, however, that the function of many such agreements is to lock in existing trading relations, in which case Mr Beattie is comparing post-agreement trade flows against the wrong counterfactual.