We're the EUs most important customer, certainly in the case of France and Germany. We are a relatively rich, geographically close economy, who are paying full whack for their expensive luxury goods, (eg cars and champagne). This makes it extremely important for them that they don't piss us off, and economic suicide for them to engage in some sort of trade war with us. Tariffs hurt them in two ways, because they risk alienating a really important market (will the British people continue to buy their stuff if they are seen as responding vindictively to a democratic vote) and their goods become more expensive than their competition. French farmers and German car manufacturers would be in open revolt if this was even suggested, and the Eurozone would be plunged into an even deeper crisis. It aint happening.