The European Commission's October Forecast has predicted if the country left the EU without a bargain that "would mean sudden changes in trade relations between the UK and the EU after April 2019 and the economies on both sides of the Channel ".
Marco Buti, Director General for Economic Affairs and Finance, said in a letter at the beginning of the forecast that no deal will affect the UK.
He said: "In the case of nothing scenario, the effect is expected to be much more on the UK than on the EU as a whole."
The report specifies that their prospects are based on current "status quo" discussions, but there are no ongoing discussions.
It states that the UK will be worse off if there is no fruitless trade outside EU customs and single market unions.
It adds: "The uncertainty about the UK status outside the EU in the future is expected to boost the growth of the UK.
"There are major risks to the prospect, especially in the case of a scenario.
"In general, the results of the relevant studies show that Brexit is a situation of economic loss of losing."
However, the report suggests that the recent sterling pound conflict against the euro is that the optimism of investor in Brexit is a success.
He reads: "In terms of the sterling pound, the perception of a more optimistic investor in the outcome of Brexit's discussions could also contribute to the recent repayment of the sterling pound against the euro."
The report also anticipates that the UK will be the country that grows next year next to Italy.
He warned that the growth of the United Kingdom will continue to be overseen by 2019.
The body said: "Private drinking growth is anticipated to remain weak as real wages grow moderately and households are looking to maintain savings.
"Extensive uncertainty means that the growth of investment in business is likely to continue to restrict."