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."