British opposition leader Ed Miliband plans to criticize Prime Minister David Cameron's referendum plans Monday, saying efforts to separate Britain from the European Union could close Britain off from the world and put jobs at risk for millions of people. He hoped to appeal to business leaders, saying the threat of secession could promote uncertainty among businesses and investors. Miliband’s office has released excerpts of his speech.

"Leaving the single market and stepping away from a trading block that strengthens Britain's ability to work with the new economies, like Brazil, India and China, would be a disaster for our country," he plans to say.

"It would risk businesses billions of pounds in lost profits. It would risk millions of jobs. It would make Britain weaker, not stronger, in the world."

Cameron plans to hold a referendum by 2017 on whether the United Kingdon should remain a part of the European Union. Cameron has said he will support an in/out referendum if Conservatives are re-elected in general elections next May.

Meanwhile, Miliband’s political future is also uncertain. Pundits say the opposition leader is focusing on the impending referendum to turn attention from issues within his own party. Labor party member Simon Danczuk told BBC One's "Sunday Politics" while Miliband leads the ticket, polls indicate he is not a popular candidate, and Labor MP Andrew Mackinlay said Miliband should step down. A recent poll by YouGov indicates Miliband has lost favor with Labor voters.

Still, many Labor members of parliament continue to endorse him. London Mayor Ken Livingstone said Miliband could be as significant a prime minister as Margaret Thatcher.

Businesses have deeply opposed the Labor party in the past because of policies including a price freeze on energy companies and hikes in top rate for income tax. The party has largely been deemed "anti-business." However, Miliband's appeal is seen as an effort to change that sentiment.

"If I am prime minister I will never risk your businesses, British jobs, or British prosperity by playing political games with our membership of the European Union," he plans to say in his speech.