When Britain decides on Thursday whether to leave the European Union, London's voice may prove decisive. But for which side?

Britain's capital, home to almost 9 million people, encompasses some of the most pro-EU places in the country — and the least.

In the cosmopolitan City financial district, where almost half a million people from around the globe work in Europe's biggest financial center, pro-EU sentiment predominates. But just a few miles away the borough of Havering, stronghold of working-class East Enders, topped a national survey of the most anti-EU places in Britain.

The two districts represent the opposing views at the heart of Britain's EU debate. One sees the bloc's free flow of people and money as a benefit. The other sees it as a threat.

Fishmonger David Crosbie, working on a drizzly morning in Havering's outdoor Romford Market, is an emphatic "leave" supporter. For Crosbie, the decision has a lot to do with borders, on land and sea. He says he is tired of European fishermen trawling waters around Britain under the EU's Common Fisheries Policy.

"French, Portuguese, Swedish, Dutch — whatever. They can all come. They go right up on the beach," he said. "Plus there's no immigration control. Anybody can come over here, skilled or unskilled."

Immigration has become the most emotive issue of the campaign leading up to Thursday's referendum, stirring fears of instability among voters and drawing allegations of xenophobia from "remain" supporters.

The EU is built on the principle that citizens can live and work in any of the 28 member states. Since the bloc expanded to include former communist countries in eastern Europe more than a decade ago, hundreds of thousands of people have moved west to Britain and other wealthier EU nations.

The perception that EU migrants come to take jobs — and, somewhat paradoxically, to live on welfare benefits — is driving "leave" sentiment in Havering and other Euroskeptic areas.

But 15 miles (24 kilometers) to the southwest in the historic heart of financial London, policy chief Mark Boleat argues that thousands of jobs, and London's standing as a financial center, depend on the EU.

"The European Union has been good for the country generally, very good for financial services," said Boleat, who heads the policy committee at the City of London Corporation, which runs the financial quarter. "Many jobs depend on it, and we think that leaving the European Union will be taking a significant risk."

That view is backed by the Economist Intelligence Unit, which said last week that leaving the EU would endanger London's status as a global financial hub, "almost certainly depriving U.K.-based financial firms of their passport to conduct business anywhere in the EU."

Boleat said that in the City, "we accept we're part of a global community and we benefit from it. But that view is not shared everywhere."

Built on the ruins of Roman and medieval London, the City radiates solidity and wealth, with its glass office blocks and imposing brick and stone buildings, including the huge, 18th-century Bank of England.

Havering — a chunk of suburban Essex county absorbed into Greater London in 1965 — is a workaday place of 20th-century houses and strips of shops on busy roads. Many residents are Cockneys who moved out of London's East End in search of more space and quiet, or their children.

It's not the poorest part of London but it is one of the least ethnically diverse — 83 percent of people identify themselves as "white British," compared to 45 percent in London as a whole. Almost 90 percent of Havering residents were born in Britain, compared to 63 percent for all of London.

Like other local authorities, Havering Council has had its central government funding slashed under austerity programs aimed at reducing the national deficit. Services such as meals-on-wheels, child care and garbage collection have suffered cuts. Meanwhile, rising property prices and rents mean that many struggle to find good housing, and subsidized public housing is in short supply.

"We've been told there is austerity, we must cut back," said Lawrence Webb, a Havering councilor for the anti-EU U.K. Independence Party. "The two budgets that haven't been cut are our membership fee of the EU and foreign aid. Our view is that money should be spent here. So stop giving Brussels a single penny until we sort our own economy out."

"Remain" campaigners say government austerity is rooted in the 2008 financial crisis and in British politicians' choices, not the EU.

And the origins of London's housing crisis stretch back decades, to 1980s reforms that gave public-housing tenants the right to buy their properties. Many council-owned houses and apartments passed into private hands, and few have been built to replace them.

Nonetheless, migrants and the EU often take the blame in Havering, where many people say they don't see the benefits of immigration.

"They say (immigrants) contribute toward the economy," said Jackie Duvall, a market researcher. "I don't doubt that, but at the end of the day, where is the money going? Where are all the extra taxes going? Is it going to hospitals? No. Education, the prison service? It's going nowhere. So it's a con trick."

That view is less common in central London — and not just in the financial district. In multiethnic inner-city areas such as Camden and Islington, it's rare to spot a "leave" sign.

Amy Wilson, a 27-year-old technology consultant in the City who is "strongly 'remain,'" said "leave" supporters, who tend to be older, are motivated by an unrealistic sense of nostalgia.

"I think the younger generations know that things can't go back the way they were," she said. "Because we live in a very interconnected world now, and we can't live in silos."

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