A senior official brought in to oversee the new MPs' expenses system has quit his post, saying he left the job for the sake of his "health and sanity".
Nigel Gooding resigned as interim operations director of the Independent Parliamentary Standards Authority after rows with MPs, the Mail on Sunday says.
He told the paper he had left his post three months early to take a break he "desperately" needed.
But he denied he had been hounded out by MPs angry at changes to the system.
"I have left the job for the sake of my health and sanity. I was given the option of doing another three months with IPSA [Independent Parliamentary Standards Authority] but I felt I was just too drained to carry on," Mr Gooding told the Mail on Sunday.
"I have decided to take a break that I desperately need."
New rules governing MPs' expenses - drawn up after the expenses scandal and an independent inquiry into the whole system - have come into force for the new Parliamentary session.
But IPSA - the expenses watchdog - is facing a backlash from some MPs claiming the new rules are overly complicated and draconian.
Last month, it agreed to pay cash advances of £4,000 to cover office and travel costs after MPs complained they did not have sufficient resources to cover bills for office equipment, stationery, transport and hotel accommodation.
Other MPs have been arguing the £110,000 annual staffing budget is too tight now that MPs are are being asked to pay pensions contributions personally rather than out of a central fund. They say the extra costs could result in staff being laid off.
Labour MP Paul Farrelly wrote to Mr Gooding two weeks ago, describing the new system as "prehistoric, amateurish, self-defeating and bureaucracy gone mad".
"The transition from the old system has been really poorly managed and administered," he said. "It has been consuming a lot of people's time.
"I came across one MP who seemed to be on the edge of a nervous breakdown because of all this."
Mr Gooding confirmed that the new watchdog was "a challenging working environment".
But he added: "I spent years as an amateur football referee. I have been called a lot worse on the football pitch than I was at Westminster.
"I am looking forward to relaxing for a few weeks and watching the World Cup."
Commenting on Mr Gooding's departure, a spokesman for IPSA said: "Nigel was an interim appointment and was appointed to oversee the operations from the planning through to the start-up phase, which he has done.
"Now he has made arrangements to move on."