It was also the top allegation in October and November with 44 and 40 reports being made respectively.

In Q4 (October to December) the FCA received 249 new whistleblowing reports - 83 a month or almost three a day on average. The reports contained 649 allegations in total.

The quarterly figure was a fall of 27 on the same period in 2022 and 31 lower than the 280 whistleblowing reports in the previous quarter of 2023.

The details are revealed in the latest whistleblower figures for the fourth three months of the year released by the FCA.

'Fitness propriety' was the second highest allegation in December, November and October with 26, 40 and 33 reports being made respectively.

The FCA said: “We assess every whistleblowing case we receive that falls within our remit, to inform our work and help us identify actual or potential harm. This could be harm to consumers, to markets, to the UK economy or to wider society.”

The regulator’s whistleblowing team receives reports by telephone, email, an online reporting form, and post.

It said protecting the identities of the whistleblowers who contact the FCA is vital. “We understand individuals may be hesitant to share their personal information with us when making a disclosure.”

The regulator said it is helpful when whistleblowers provide it with an ongoing contact option such as a phone number and/or email address. “This allows us to re-engage and develop on disclosures and ask further questions. We can also keep individuals informed on how we can protect their identity while we carry out our work.”

Almost half the new reports it received in 2023 Q4 came through its online reporting form.

In December around a quarter of whistleblowers opted to report anonymously, with 58 providing their identity and 19 choosing to remain anonymous.