Swiss investment bank UBS warned its clients on Tuesday it may fail to execute some orders on its electronic trading platform should this week's Brexit referendum affect liquidity or cause extreme volatility. The UK votes on Thursday on whether to stay or leave the European Union. Results, expected from early on Friday, are expected to spark frantic moves on financial markets, especially sterling. UBS said that regardless of the outcome, there could be an increase in volatility and an impact on trading volumes, which in turn could affect its ability to execute clients' positions. "In the event that extreme market moves occur, giving rise to limited liquidity in certain currencies, we may not be able to fill limit orders or take profit orders at the levels, or using the methodologies, expected in normally-functioning markets," the bank said. UBS, one of the biggest players in the $5 trillion a day global currency market, added: "In the event that extreme market moves occur in an environment of limited liquidity, our principal spreads may widen for both electronic and voice trading, liquidity may reduce and prices may turn indicative (i.e., non-tradable) for periods of time." Earlier this week, Dutch lender ING and French bank Societe Generale sent similar letters to their clients, showing the scale of concern around Thursday's referendum and the prospect of sharp one-off moves in sterling. The pan-European exchange operator Euronext also plans special measures in anticipation of higher volatility and trading volumes. Such warnings have become more common since the dramatic moves in the Swiss franc in January 2015, which led to conflicts between banks and their clients due to the absence of market prices for several minutes. Algorithmic client execution orders and Auto orders also would not be executed during any periods of indicative pricing, UBS said, referring to trading systems that use mathematical models and formulas to make high-speed transactions. Orders would be filled once normal trading resumed, the bank added.