The Commons expenses watchdog has quit after coming under fire for refusing to name MPs being investigated for dubious claims.
Luke March has resigned as the Independent Parliamentary Standards Authority's (Ipsa) compliance officer with immediate effect.
The move followed an interview with the Press Association last week in which Mr March argued that details of his probes should remain secret.
He said it would be "unfair" to identify MPs before allegations were proved, and suggested there should be no publicity at all if they were cleared.
Mr March appeared to be contradicting transparency guidelines set by Ipsa, which indicate that politicians should be identified when a formal probe is launched, and cases should be heard in public where possible.
A statement on the body's website revealed that Mr March, who had only been in the post two months, tendered his resignation last Wednesday.
In a letter to chairman Sir Ian Kennedy, he wrote: "As I explained during our conversation, after much thought and with a good deal of regret, I have come to the conclusion that the role of Compliance Officer for Ipsa is not the right role for me.
"On that basis, I have decided that the sensible thing for me to do is to resign the post."
Sir Ian replied: "Thank you for your letter of July 27 and for notice of your resignation from the post of Compliance Officer.
"I accept, with regret, and understand your conclusion that the role is not the right one for you. I know you did not reach this conclusion lightly or hastily."
Martyn Taylor, previously Ipsa's head of governance, has now become its third compliance officer in little more than a year.
He will fill in for six months until a permanent successor can be found.
Ex-RAF officer Alan Lockwood was given the post on an interim basis when Ipsa took charge of Commons expenses after the General Election.
Mr March was part-way through probes into a number of MPs' claims.
Liberal Democrat Bob Russell is the only named subject so far. He disclosed the fact himself in May, and the case was later dropped.