After 20 years of talks, Europe and the South American customs union Mercosur have signed a sweeping free-trade deal worth almost €90 billion a year which will create a market for goods and services covering nearly 800 million consumers making it one of the largest trade agreements in the world.

A breakthrough in the two-decade-old negotiations emerged earlier in June when top EU trade officials and their counterparts from the Mercosur group of nations - Argentina, Brazil, Paraguay, and Urugu...