View of the City of London | BERTRAND LANGLOIS/AFP/Getty Images City goes silent on Brexit There is wide disagreement among banks on what to say or do publicly ahead of the referendum.

LONDON — It’s the game of a lifetime between the United Kingdom and the European Union but some of the City of London’s biggest players are sitting on the sidelines.

The financial sector, one of the key drivers of Britain’s economy, is deeply divided on how to influence voters’ decisions in the planned referendum on the U.K.’s membership of the EU. The City’s involvement, or lack of it, will be an important factor in the referendum campaign, especially at a time when polls suggest the outcome will be close and the most recent survey showed falling support for EU membership among U.K. business executives.

With a few exceptions, largely among hedge fund managers angry at Brussels' moves to regulate the industry, most big financial companies privately agree that a "Brexit" from the EU would be bad business for them and their customers. But there is wide disagreement on what to say publicly ahead of a plebiscite that could take place as early as this summer.

On one hand, large U.S. banks such as Goldman Sachs and Citigroup have been open about the benefits of EU membership, pointing to the job losses, financial consequences and logistical hassle that would be caused by the erection of a border between Britain and the European single market.

“We have been fairly outspoken that Citi is in favor of the U.K. staying in,” Alan Houmann, head of government affairs for Citi in Europe, the Middle East and Africa, told POLITICO. “We see the value of the single market as very high indeed from both our perspective and the perspective of our clients.”

"We see the value of the single market as very high indeed" — Alan Houmann, Citi

But large domestic players, such as HSBC and Lloyds, have studiously avoided taking a position, even though some of their senior people have spoken out on the subject. That’s because the referendum promised by Prime Minister David Cameron is stirring strong emotions in a country with a historically tortuous relationship with a bloc many Brits simply call “the Continent.”

British banks are reluctant to talk about their Brexit position, but people familiar with their views explain their silent treatment of the referendum by pointing to one key difference from their foreign rivals: individual customers. Whereas Goldman, Citi and their U.S. competitors look after large businesses and fund managers who tend to support Britain’s membership of the EU, the likes of Lloyds and HSBC have millions of mom-and-pop clients whose views on Europe range from the enthusiastic to the rabid.

“The banks’ position is understandable. They just don’t want to offend their checking account customers,” said a City figure. Some banks say they are waiting to see the outcome of the deal Cameron can wrangle from his European counterparts — which could be sealed at next month’s EU summit — before taking a public stance.

Anti-banking sentiment

Both supporters and opponents of Brexit seem to agree: the big High Street banks won’t be much of a factor in the referendum. “We are not expecting the big U.K. banks to come onboard with Vote Leave. But we also don’t expect the big banks will be campaigning for staying,” said Paul Stephenson, communications director for Vote Leave, one of the two groups pushing for an Out vote. “I expect most banks will stay out of it.”

In theory, that should leave foreign banks, which have tens of thousands of employees in the U.K., free rein to speak for a sector that accounts for more than 8 percent of Britain’s GDP and employs some 1.1 million people.

That could be an uncomfortable position in a country where anti-banking sentiment among politicians and the public is still running high. Pro-Brexit campaigners are already planning to seize on any EU-friendly utterance from foreign banks.

“Despite the musings of some international investment banks, British withdrawal from the EU would actually cement Britain’s dominant position not undermine it,” reads a report to be released in the next few days by Leave.EU, the other pro-Brexit movement. “Indeed financial services is to Britain what viniculture is to France. Would the French let the EU dictate wine regulation?”

Behind the scenes, supporters of the In vote are working to defuse such claims. Roland Rudd, the public relations guru who is treasurer of Britain Stronger in Europe, told POLITICO that his campaign is working to shield individual companies from criticism by creating a common platform to air their views. “The key thing is getting particular industries to support our campaign so it is harder for the Out campaigns to pick them off one by one,” he said.

In campaigners in the City want big financial groups to speak up early because they are wary of a repeat of the chaos that preceded the Scottish referendum in 2014. In that case, a large part of the financial community stayed silent for much of the campaign and spoke out on the dangers of a disunited kingdom only in the immediate run-up to the vote, when it appeared that supporters of an independent Scotland could win.