UK stepping into ‘black hole’ with Brexit: Sorrell

With the U.K. referendum on its membership of the European Union fast approaching, several high profile names have detailed what a "Brexit" could mean for the country.

WPP CEO Martin Sorrell told CNBC on Monday that "you're better off trying to change the rules of the club inside rather than banging on the door outside."

Sorrell said that most of the advertising giant's clients believe a Brexit would be damaging for the economy, certainly in the short to medium term.

"Long term, we don't know. We're sort of stepping into a black hole, so being part of the European community … I think is economically the best case," he said.

On issues of immigration and terrorism, the WPP chief said that's where the debate gets "very emotional."

"As a second-generation immigrant, my own view is that immigrants add benefit to the economy," he said.

British citizens are due to vote on June 23 on their country's future relationship with the EU. In an interview from Washington on Friday, British finance minister George Osborne told CNBC that "leaving would cause an economic shock and a long-term economic cost for the U.K."

Osborne added that the referendum is "a big democratic exercise" that helped to resolve uncertainty about the U.K.'s role in the EU. He told CNBC that he hopes Britain will remain in the union and then "get to work on reforming the EU."

EU and British flags
Krisztian Bocsi | Bloomberg | Getty Images

Bookmaker Ladbrokes is predicting a 33 percent chance that Britons will vote to leave the European bloc. The fierce debate has strained relationships and seen major political heavyweights like Prime Minister David Cameron and London Mayor Boris Johnson put forward opposing views.

Analysts at Credit Suisse in January said a Brexit would result in an "immediate and simultaneous economic and financial shock for the U.K." It added that it could see a drop in business investment, hiring and confidence. The Confederation of British Industry released new independent research last week showing it could cost the economy £100 billion ($142 billion) and 950,000 jobs by 2020.

Meanwhile, the "leave" campaign points to pressures on the U.K.'s state-run national health service, the threat of terrorism and the costs of EU membership. The current concerns over the country's steel industry has added more fuel to the debate, with some claiming tight EU regulations has limited the government's response.

UBS Chairman Axel Weber seemed to agree with Osborne, telling CNBC, "If you look at a European debate without the British, it would be a debate between Germany, Italy, France and the other member countries."

"I think we would lose a lot of colour in that debate, be it the attitude towards capital markets, be it the entrepreneurial orientation that the British and German societies have and all of these discussions would be much more difficult, so I think that's where the fragility around some of these political debates that could impact not just on Europe but beyond is really a concern in a situation where growth is fragile and can easily be derailed by such discussions," he said.

China's vice finance minister told CNBC that the Chinese government "strongly support(s) a strong and unified EU."

Speaking from the International Monetary Fund's spring meetings, Zhu Guangyao pointed to the strong interdependence of the integrated global economy, and warned against breaking away from a larger economic bloc.

"We must strengthen our dependence and strengthen our macroeconomic policies in particular," he said.

President Barack Obama will arrive in the U.K. later this week. As well as wishing Queen Elizabeth a happy 90th birthday, he is expected to touch upon the topic of Brexit in favor of the U.K. staying in Europe.

Osborne on Monday published a column in The Times stating that leaving the EU will cost the average British family an extra £4,300 ($6,082) per year.

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