The Financial Conduct Authority received 491 complaints in the year to November 2015.
The flow of complaints against the regulator was even all year, with 246 made between December 2014 and 31 May 2015, and 245 between 1 June and 30 November 2015.
The FCA’s latest data bulletin says the regulator did not investigate 47 per cent of the allegations.
It says: “This can be for a variety of reasons, including that the complaint is a general expression of dissatisfaction where no misconduct has been alleged, or that the allegations are excluded, referred, deferred or outside of our scope.”
The regulator investigated 291 allegations, of which 42 per cent were fully or partly upheld and 58 per cent were dismissed.
The regulator has not published complaints data for 2014.
The FCA also reviewed 1,108 complaints about financial promotions between 1 July and 30 September 2015, down 69 per cent on 3,604 in the same period of 2014.
The majority (65 per cent) of the 2015 cases related to consumer credit.
The regulator took action in 34 cases in the 2015 period and 181 in the 2014 timeframe.