Keir Starmer has demanded Liz Truss turn down a £115,000-a-year fund she can claim for life - despite just 44 torrid days in office.
The 47-year-old is eligible for the annual allowance until she dies, even though she was the shortest-serving PM in history.
Separately she will also trouser an £18,860 payout for leaving office - double the £9,094 she was actually paid while on the job.
But she’d miss out on a special Prime Ministerial pension worth half his salary, as the bumper packages were scrapped in 2013.
The Public Duty Cost Allowance pays for office costs necessary for ex-PMs’ “special role in public life”. It pays for office and secretarial costs, not any personal expenses, and has to be claimed back against actual spending.
Government officials confirmed to the Mirror there is no minimum period PMs must serve to be eligible.
Labour's leader told ITV's Good Morning Britain: "She should turn it down. I think that's the right thing to do.
"She's done 44 days in office, she's not really entitled to it, she should turn it down and not take it."
Lib Dem MP Christine Jardine warned it will “leave a bitter taste in the mouth of the millions struggling with spiralling bills.”
She added: “Truss’s legacy is an economic disaster - for which the Conservatives are making taxpayers foot the bill.
“For Truss to walk off into the sunset with a potential six figure dividend, while leaving the British public to suffer, would be unconscionable."
The PM's deputy spokesman said: "I have to point you to the convention and what that is, which is an allowance that is available by convention for Prime Ministers for their future office."
The spokesman declined to comment on what Ms Truss's arrangements are once she is no longer PM.
John Major and Tony Blair both claimed the full £115,000 in 2019-20, while Gordon Brown claimed £114,802 and David Cameron claimed £111,457.
Theresa May - who as a sitting MP can access Parliament’s staffing budget - claimed less at £34,836.
Boris Johnson set up The Office of Boris Johnson Ltd two weeks ago with the intention to start claiming on the fund.
If he scores a surprise comeback as Prime Minister his £115k fund would be “reviewed in relation to the remuneration” he receives as PM.
