Britain and the European Union (EU) would face a combined annual bill of around £58 billion ($80.4 billion) if Brexit talks were to collapse without a new trade agreement in place, according to a new study.
The report, published Sunday by consultancy firm Oliver Wyman and law firm Clifford Chance, said the cost of a so-called "no deal" scenario would total around £31 billion for EU exporters and around £27 billion for U.K. exporters. It implies that firms on both sides of the equation would be hit by new tariffs if a trade deal fails to be agreed.
"We see the best-prepared firms taking hedges now based on the direct impacts on themselves, their supply chains, customers and competitors. Unfortunately, we see that small firms are least able to take these steps at present," Kumar Iyer, partner at Oliver Wyman, said in the report.
The EU's automotive industry was seen to incur the biggest costs if Britain and the bloc's trading relationship reverted to World Trade Organization (WTO) rules post-Brexit, the report said. Meanwhile, the U.K.'s financial industry looked likely to "take the biggest hit by far," it claimed.
Britain's governing Conservative party has said the U.K. will exit both the single market and the customs union when the country leaves the bloc next year.
The EU's customs union is a trade agreement that eliminates customs duties between EU member states. The single market is a deeper form of co-operation between member states that allows the free movement of goods, services, money, and people in the bloc.
Last week, the EU laid out its draft guidelines for upcoming trade talks between the two sides. The draft, circulated on Wednesday by European Council President Donald Tusk, warned Westminster that Britain's current position would likely result in "negative economic consequences."
Tusk added the looming prospect of a free trade agreement could represent the first in history that actually loosens economic ties.
One way in which both sides might be able to mitigate the impacts of post-Brexit trade barriers would be to consider a future customs arrangement equivalent to the EU's customs union, the impact assessment said.
A future trade deal which largely mimics the EU's customs union was thought to reduce the annual cost of Brexit to around £14 billion for the EU and approximately £17 billion for the U.K.
Britain's Labour party has recently shifted its stance to advocate that the U.K. should remain in the customs union post-Brexit.
"Given the difficulty of knowing exactly what turbulence lies ahead many businesses are putting Brexit in the 'too hard' box," Jessica Gladstone, partner at Clifford Chance, said in the report.
"However, exporters that understand exactly what Brexit's risks and rewards could be for them will be able to implement the right plans at the right time to ensure that they are one of the winners rather than one of the losers," she added.
The U.K. is poised to leave the EU on March 29, 2019.
— CNBC's David Reid contributed to this report.