Swiss bank UBS issued a warning on June 21 that it may have difficulty accommodating trading in the run-up to, and in the wake of, this week’s UK vote on European Union membership.

UBS said in an emailed notification that while it's difficult to predict market conditions just before the June 23 vote and immediately after results are expected the following day, "we may see an increase in volatility and an impact on trading volumes". That could lead to a situation where prices become "non-tradable" for certain periods, the bank said.