West Ham football club sponsor and currency broker Alpari has shut its UK arm following the Swiss National Bank's decision to end its capping of the Swiss franc against the euro.
The foreign exchange broker said in a statement that the move had created "exceptional volatility and extreme lack of liquidity".
As a result, the majority of Alpari clients had "sustained losses".
The euro rose 1.2% on Friday to buy 0.9869 Swiss francs.
Thursday's euro-franc close was 0.9755, well above its lowest point of 0.85 following the sudden removal of the cap.
"Where a client cannot cover this loss, it is passed on to us," it said. "This has forced Alpari (UK) Limited to confirm today that it has entered into insolvency."
The Financial Conduct Authority said it was "working closely" with the company.
West Ham said Alpari's collapse would not affect the club, which was in talks with potential new shirt sponsors for next year.
The SNB shocked markets on Thursday by reversing a three-year-old policy.
The bank had previously capped the value of the franc at 1.20 per euro.
FXCM shares suspended
At one point on Thursday, following the decision to abandon the cap, the franc soared more than 30% against the euro.
Derek Halpenny, a currency strategist at Bank of Tokyo-Mitsubishi UFJ, described the currency move as "unprecedented".
The euro regained some ground on Friday, rising 2.5% to 1.01 francs.
Alpari, which signed a £3m, three-year deal with West Ham in 2013, is one of a number of companies to be affected by the volatility caused by the SNB's action.
Shares in US forex trading group FXCM were suspended shortly before trading began in New York on Friday after the stock plunged by 90% in pre-market dealing.
FXCM said on Thursday it might not be able to meet certain regulatory capital requirements due to "unprecedented volatility" after clients suffered losses of $225m.
The US market regulator, the National Futures Association, said it was in "constant contact" with FXCM.
"We've been watching the volatility in light of the activities that occurred early yesterday morning, so we are monitoring all of our firms," a NFA spokesperson said.
Analysis: Jonty Bloom, business correspondent
The Swiss National Bank's decision on Thursday to abandon attempts to fix the Swiss Franc against the euro resulted in the "Swissie" rising by 30%. It was probably the largest one-day movement by a major currency since the First World War.
The reasoning for the move were fears that the eurozone will soon start printing money. That is almost certain to cut the value of the euro and boost that of safe haven currencies, such as the franc. In short, the Swiss could no longer afford to hold the line.
The consequences are just beginning to be felt. Alpari, one foreign exchange broker, has gone bust, while another has lost £30m.
Yet it is the Swiss who have lost most, as the cost of their exports will now soar.
If you were thinking of treating yourself to a nice Swiss watch for the new year, you might want to check your bank balance first. It is likely to be 15% more expensive than it was on Wednesday.
New Zealand foreign exchange dealer Global Brokers NZ was also forced to close due to hefty losses incurred from the currency turmoil.
Following the closure, New Zealand's Financial Market Authority said it would "be seeking assurances that the client funds have been protected and segregated."
Other forex companies also suffered losses. IG Index said it would lose some £30m following the turmoil.
CMC Markets also recorded losses, but chief executive Peter Cruddas said the overall impact had not materially affected the group. "It's business as usual," he said.