Britain's 2.2 million financial industry workers face years of uncertainty and the risk of thousands of job cuts after the country voted to quit the European Union, leaving question marks over London's status as Europe's premier financial center.
The 'Vote Leave' campaign fronted by a slew of Conservative lawmakers and financial industry veterans claimed victory over its 'Britain Stronger in Europe' rival, after 52 percent of Britons voted to support their plan to leave the 28-nation club.
A morning of triumph and jubilation for the Brexit camp has been overshadowed by an average 21 percent fall in the share prices of the top five British banks and falls of between 20-32 percent at elite wealth managers Schroders, Aberdeen Asset Management and St. James's Place.
Euro stoxx bank futures had earlier indicated record falls of 18 percent.
A leave vote means the future of Britain's financial services industry is now hanging in the balance.
All depends on the divorce between Europe and Britain, the latter's ability to retain access to the European free market, and cope with the volatility that has seen sterling nosedive against major global currencies.
Mood in the restaurants and coffee shops in the high-rise banking hub of Canary Wharf, home to JPMorgan, Citi, HSBC and Barclays, was sober and contemplative, with job security fears rising to levels unseen since the 2008 financial crisis.
Investment banks have already warned they could move thousands of jobs if Britain opts out of the EU, while the European Central Bank has signaled it could force euro trading out of London, the world's largest foreign exchange market.
But some sought to play down fears of a catastrophic hit to Britain's banking sector, pointing to extensive contingency planning and many years of experience navigating crisis.
Lloyd Blankfein, Chairman of Goldman Sachs and Jes Staley, CEO of Barclays - which suffered the biggest one-day fall in its share price on record on Friday - said their banks had long histories of adapting to change and would work with relevant authorities as the terms of the exit become clear.
HSBC Chairman Douglas Flint said the day marked a new era for Britain and British business, describing work to establish fresh terms of trade with our European and global partners "as complex and time consuming."
Wall Street bank Morgan Stanley said the significance of the decision would not be known for some time.
A person familiar with the matter earlier told Reuters it could move around 1,000 of its roughly 6,000 employees currently in Britain to elsewhere in Europe if Britain quit the EU.
Jamie Dimon, CEO of rival JPMorgan told staffers his bank "may need to make changes to our European legal entity structure and the location of some roles to comply with new laws as we serve our clients around the world", casting a pall over its 16,000 strong workforce.
However the City of London Corporation, which oversees the capital's financial district, said the leave vote should not lead to a major exodus.
"There will be no mass exit of banks and financial institutions from the Square Mile," Mark Boleat, policy chairman for the City of London Corporation said in statement.
"The general view of the City is that the government should push for the UK to retain our access to the single market," Boleat said.
The British Bankers Association Chief Executive Anthony Browne moved to reassure people that banks across the country would be operating as normal on Friday.
"People will be able to take money out of cash machines, exchange currency and have full access to their banking services," he said.
CARNAGE ON MARKETS
Months of bitter campaigning has left the industry - which earned the nation 190 billion pounds in 2014 - divided, with investment banks and insurers pitted against many fund managers and brokers who wanted a Brexit.
Property investor Richard Tice, a co-founder of Leave.eu, a British Out campaign, and one of the few prominent City figures in favor of leaving, told Reuters he cried tears of joy after the vote.
"There is huge joy, delight and pride. We have changed the course of history in the UK. It is very simple, everyone needs to calm down and do what we do well which is working and playing hard."
But there was little of that joy in trading rooms.
Sterling fell to its lowest level since 1985, the year before Britain's deregulation of financial markets that helped propel the City of London into one of the world's major financial centers in the so-called 'Big Bang'.
All the major international and British banks in London had traders either working through the night or on call.
"Leave's victory has delivered one of the biggest market shocks of all time ... Panic may not be too strong a word," Joe Rundle, Head of Trading at ETX Capital said.
Sources at banks said memos emailed internally to rattled employees advised them to think about clients first.
"I've convened a big team meeting at 0800 GMT as the juniors are freaking out. I will tell them to focus on their job and wait for the volatility to pass but the reality is much, much starker, we'll have a crash and big layoffs," a senior investment banker at a U.S. bank told Reuters.
"It's an act of national self-harm," he added.
Many financial firms rely on the EU's 'passporting' regime to sell their services across all of the bloc while basing the majority of their staff and operations in London.
European government officials said UK-based firms could lose these privileges in the event of a Brexit, a move that would force them to shift some of their operations to the likes of Frankfurt, Paris or Dublin if they wanted to serve EU clients.
The Bank of England said it had undertaken extensive contingency planning and will take all necessary steps to meet its responsibilities for monetary and financial stability, in conjunction with HM Treasury, other domestic authorities and overseas central banks.
The Financial Conduct Authority said it would not comment about any immediate action it might take until after the result has been formally announced. The Bank of England's Prudential Regulation Authority said it had no comment for the time being.
Some commentators said the volatility would be temporary and would soon subside when international investors drawn by a fall in sterling began to scour financial markets for bargains.
"Certainly, some international investors could find the UK less attractive but history shows us others are positively attracted to economies that get a devaluation boost," said Colin McLean, Managing Director at SVM Asset Management.
"There may even be more takeover activity from overseas firms looking for bargains on the London stock market," he said.
Disappointed supporters of the EU project on mainland Europe said Britain would struggle to keep the same market freedoms that have attracted more than 250 foreign lenders to its shores.
"If Britain guarantees to implement all the rules, then Europe will unlikely punish London," said European Parliament member Sven Giegold, a member of the German Green Party.
"But the will of the citizens was exactly to get rid of that dependence. That is the irony because you can't do both. If you want to keep your market open, you have to accept all the rules. Without that, Europe would be foolish to extend privileges to the UK and the City of London," he said.
(Additional reporting by Carmel Crimmins, Richard Leong and Olivia Oran in New York, Vikram Subhedar, Freya Berry, Simon Jessop, Anjuli Davies, Carolyn Cohn, Maiya Keidan and Huw Jones in London; Editing by Rachel Armstrong)