The chief constable of Sussex, Martin Richards, is being investigated over an allegation of misconduct.
The Independent Police Complaints Commission (IPCC) is looking into an anonymous claim that Mr Richards used his position improperly to exert undue influence over a police operation.
He has not been suspended while the investigation is carried out.
Sussex Police Authority said that it carefully considered the allegation of misconduct through its Professional Standards Committee before referring it to the IPCC last month.
It said that it made the decision to refer the matter to the IPCC in light of Mr Richards’s seniority.
It said: “The decision by the authority to refer the allegation is a neutral act and does not reflect any assumption of wrongdoing.
“While the investigation is under way and until the facts are established, there should be no assumption of impropriety or speculation on the outcome of the investigation.”
The chairman of the Professional Standards Committee, Dr Gordon Bull, said: “Trust in the integrity of the police is essential and is of ongoing legitimate public interest.
“Given the seniority of the officer subject to this allegation it is absolutely right that the police authority has voluntarily referred the matter to the IPCC for independent scrutiny.”
Sussex Police Authority and Sussex Police said that they strongly supported transparency and public scrutiny, announcing involvement in IPCC investigations proactively whenever possible.
In this instance, they said that they had delayed an announcement because of the risk of a potential impact on an ongoing operational matter.