One of the leading think tanks of the U.K., Open Europe, announced that the cost of the U.K. exiting the EU and closing its borders to European citizens would cost, on average, $84 billion annually until 2030. In the report issued by Open Europe containing possible case scenarios for the U.K. to exit the EU on Jan. 1, 2018, it was stressed that the gross domestic product (GDP) of the U.K. may decrease by 2.2 percent. The report also noted that if the U.K. exits the EU without signing the required border and trade regulations, then its total monetary loss between 2018 and 2030 will equal 672 billion British pounds.

The best-case scenario would include the U.K. signing a free trade deal with the EU and lowering its trade with the rest of the world, which would increase the U.K.'s GDP by 1.6 percent.

Open Europe Director, Mats Persson, said that when you are opening up your economy and trade to compete with the rest of the world and limit your human resources at the same time, then you will face some tough consequences. Last month, British Chambers of Commerce (BCC) General Director John Longworth said that in order to end the uncertainties in the economy, the referendum on U.K.'s EU membership should be held in 2016 instead of 2017 as originally planned, and British Prime Minister David Cameron had said that the leaders of the business world gave full support to the referendum. Cameron wants to renegotiate certain terms, mainly limiting freedom of movement within the EU if his party wins the upcoming general elections. However, European leaders claim that this would be against the EU's main principles and are objecting to Cameron's requests. Cameron wants to hold a referendum on the U.K.'s EU membership by the end of 2017 at the latest.