The customs union might survive, and develop further, if Brazil were to accept its partners' desire for lower external tariffs all round, especially on capital goods.

ECONOMIST: Another blow to Mercosur

But that might change, especially after the news of the WTO's preliminary ruling on American steel tariffs.

ECONOMIST: Will there ever be a breakthrough?

Yet for all its shortcomings, Mr Yeats's work does sound an important warning especially for Brazil, which forced Mercosur to adopt higher-than-average tariffs on capital goods while itself imposing tariffs of up to 70% on imported cars.

ECONOMIST: Trade agreements

"I don't see why agriculture always has to be the bargaining chip in Europe's trade negotiations... especially when a certain number of South American countries, notably Argentina, are putting new protectionist tariffs on food imports, " he said.

BBC: EU eases trade with Latin America at Madrid summit