Police have launched a fraud investigation at the Derry constituency office of the Speaker of the Northern Ireland Assembly.
DUP MLA William Hay reported the matter after irregular office cost payments were brought to his attention.
A member of staff at the Ebrington Terrace office in the Waterside has been suspended.
Mr Hay said: “There is no doubt that systems and procedures will have to be examined to consider how what I have fallen victim to can be prevented in future.
“However, I have to take personal responsibility for the fact that my management of affairs in my constituency office did not uncover what was happening at an earlier point.
“No one will be more critical of that than me.”
The office cost allowance provides funding to MLAs to undertake Assembly and constituency work and includes the cost of running a constituency office and employing staff.
The Speaker has spearheaded efforts to improve transparency over payments.
Mr Hay, who has been appointed to the House of Lords, said: “Last week, I contacted the Police Service of Northern Ireland to report my discovery of what appears to be fraud having been committed in my constituency office.”
This followed his own investigation after an irregular trend in payments from office cost expenditure, which he had had not previously noticed, was brought to his attention.
The Assembly has also begun its own response to suspected fraud.
The Speaker added: “I will be making no further comment on the situation within my constituency office while the criminal investigation is ongoing but I felt that I should make these comments in the interests of transparency and given my leadership role as Speaker of the Northern Ireland Assembly.”