The news came on the day of a court hearing for three Labour MPs facing charges of theft by false accounting.
The Metropolitan Police confirmed that another file of evidence relating to Parliamentary expenses has been delivered to the Crown Prosecution Service (CPS). To date, four people have been charged with expenses abuses.
Police and prosecutors declined to confirm the identity of the politician who is the subject of the file, the eighth to be passed to the CPS.
A Metropolitan Police spokesman added: "A small number of cases remain subject to consideration by the joint MPS and CPS assessment panel, or are subject to continuing investigation."
Meanwhile, lawyers for three MPs accused of abuses attended a court hearing yesterday.
David Chaytor, Elliot Morley and Jim Devine, who are suspended from the Labour Party, were charged last month, along with suspended Tory peer Lord Hanningfield.
Their lawyers said they intended to argue that they should be dealt with by Parliament rather than the courts because their actions were protected by Parliamentary privilege.
The three MPS and Lord Hanningfield are accused of theft by false accounting and if found guilty, face a maximum sentence of seven years in prison.
Further legal arguments are scheduled to take place in early May, with individual trials for each politician expected later in the year.