Bilateral trade reached $63.1 billion in 2012, surging 7.5 percent compared with the previous year amid the global recession.
Yet the referendum proposal, influenced by downward economic trends in Britain, underscores the decline in international status and the conservative-leaning tendencies of the world's sixth-biggest economy, said Zhao.
"While many in the UK —within both the Conservative Party and the Labour Party — would like to renegotiate the terms of the UK's relationship with the EU, there are not many who see the need for an 'in-out' referendum, which is what Cameron is proposing," said Richard Caplan, professor of International Relations at the University of Oxford.
"Cameron's commitment to a referendum risks generating uncertainty about the UK's commitment to Europe more broadly, which could discourage investment in the country at a time when the country is struggling to recover economically," Caplan said.
Instead of providing an instant vote, Cameron may use such a long window to bargain with the EU for a bigger share of influence in the bloc's reform process, which is currently dominated by Germany and France, or a looser version of full British membership, analysts added.
Speculation over a vote on leaving the EU rattled other members of the bloc currently focused on tackling their economic woes.
Martin Schulz, speaker of the European Parliament, said: "We need the UK as a full-fledged member, not harboring in the port of Dover. The UK can shape the EU by working with its partners."
German Foreign Minister Guido Westerwelle on Wednesday urged the UK to remain in the EU, saying in an age of globalization, all Europeans are in the same boat.
Laurent Fabius, French foreign minister, said leaving the EU could be "dangerous" for Britain. "I'll take an example which our British friends will understand. Let's imagine Europe is a football club and you join, but once you are in it you can't say, 'Let's play rugby'", Fabius said.
Going back home: A standing journey