UBS has been fined £27.6m by the regulator after misreporting close to 136m transactions over a ten-year period.
Between November 2007 and May 2017, the Switzerland-based bank failed to report a number transactions as required but also reported cases that did not require it.
The FCA says UBS failed to provide complete information on 86.67m reportable transactions and erroneously reported 49.1m transactions.
UBS also failed organisationally in its change management processes, maintenance of data and testing of reporting accuracy, the regulator adds.
FCA executive director of enforcement and market oversight Mark Steward says: “Firms must have proper systems and controls to identify what transactions they have carried out, on what markets, at what price, in what quantity and with whom.
“If firms cannot report their transactions accurately, fundamental risks arise, including the risk that market abuse may be hidden.”
The bill for UBS was originally £39.4m but the firm incurred a 30 per cent discount as it agreed to resolve the case.