By Steve Dinneen Contrary to popular belief, Cinco de Mayo is not Mexican Independence Day. That is 16 September, and commemorates the 1810 call to arms which led to the expulsion of the Spanish. It is in fact an annual remembrance of Mexico’s 1862 defeat of the Second French Empire, although today it is more a general celebration of Mexican culture, particularly its fine heritage for agave spirits. As Britain moves beyond the era of tequila slammers, the growing respectability of agave-based spirits has been accompanied by increased variety and availability. There are more than 200 species of…