Such an outcome would, however, be a shock for UK businesses engaged in deals abroad, as well as domestic prices and the employment situation, the report, obtained by the Independent newspaper, said.
New rules would mean thousands of outdated WTO tariffs, particularly in the agricultural sector, which would significantly harm UK competitiveness, according to the document.
"UK agricultural exports to the EU would face new tariffs of 14.4 per cent on average, and non-agricultural goods an average tariff of 4.3 per cent — enough to undermine the competitiveness of some UK businesses… The UK would have less access to the single market than Pakistan, Rwanda or Yemen," the report stated.
The country would also see rising prices and the government would be limited in its options to drive them down by lower import duties as this would undermine any free trade deal negotiations, the report stressed.
The Treasury declined to comment on the leak, stating that it had already published an analysis on the long-term impact of Brexit last year.
April's pre-referendum paper, described by Brexit supporters as fear-mongering, said the United Kingdom could face a year-long recession, lose some 500,000 jobs and suffer from rising inflation and falling property prices if Brexit began. The country's GDP would shrink 3.6 percent within a year with each household to be over $6,000 worse off after 15 years faring outside of Europe. The Treasury's worst-case scenario included the loss of some 800,000 jobs and a 6-percent fall in GDP within one year.
