London's market continued to boom amid political tension, with financial services exports totalling £68 billion in 2017 — more than New York and Singapore combined.
Catherine McGuinness, policy chairman of the City of London Corporation, said the U.K.'s financial services district was a "magnet" for foreign investors, helping to generate major capital projects — long-term projects that help companies build or maintain assets such as facilities and equipment.
"The U.K. leads the world when it comes to exporting financial services and we have a number of strengths that appeal to investors," she said in a press release Wednesday.
"We cannot, however, afford to take this position for granted. Foreign investment flows can shift quickly so it is vital that we secure a positive Brexit deal that provides confidence and clarity for the sector. This will help to attract investment in the future of London and the U.K."
In June, the U.K.'s Department for International Trade published figures showing that foreign investment into the wider U.K. economy fell by 9 percent between 2016/17 and 2017/18.
New investments were down by 5 percent, with mergers and acquisitions falling by 13 percent. The biggest overseas investor into the U.K. was the U.S., according to the department's report.
John Glen, economic secretary to the U.K. Treasury, told CNBC via email that he was not concerned about Brexit's impact on London's financial services district.
"The U.K. is and will remain the preeminent center for global finance, long after we leave the EU," he said. "So the fact that our financial services sector is securing more foreign investment than its global competitors comes as no surprise, and will be welcomed by the 1 million people working in the industry across the country."
"But of course our status is not taken for granted — we continue to do everything we can to maintain and enhance our world-leading position."
The City of London Corporation selected the world's top nine financial services destinations for its study.