The Commons has been criticised for not publishing the sums given to retiring MPs, and those who lost their seats, in lucrative resettlement grants.
It published a list of 220 ex-MPs who received the "golden goodbyes" - worth up to £64,766 for long-serving MPs.
But the amounts paid have not been revealed - a Commons spokeswoman said they could be worked out.
FOI campaigner Heather Brooke said the Commons was "wilfully with holding" information from the public.
"They don't feel confident to stand behind those amounts," she told the BBC.
Previous calculations by the Taxpayers' Alliance suggest that more than £10m was paid out to departing MPs last year.
Resettlement grants, nicknamed "golden goodbyes", were paid out under the old expenses system in addition to parliamentary pensions and winding-up payments given to MPs to cover costs. They were tax free for the first £30,000.
Long-serving MPs who were still of working age could receive the equivalent of a year's salary, £64,766, to help them in "adjusting to non-parliamentary life" but the payments were reduced when an MP reached the age of 70.
'In public domain'
However last year's payments were not included in the latest expenses data published a month ago, covering the last set of office costs, travel, accommodation and "winding up" costs to retiring MPs paid out by the Commons before the new expenses body took over.
This week the House of Commons Commission - a committee of six MPs chaired by Speaker John Bercow - published the names of those who were paid the grants after the 2010 election, but not the amounts received.
A spokeswoman for the Commission said the details had been published in response to a Freedom of Information request, which asked for the names, and the amounts received could be worked out.
Under Commons expenses rules, departing MPs usually get a grant of between 50% and 100% of their salary, depending on age and length of service. Those aged 55 to 64, who have served 15 or more years as an MP, were entitled to the full year's salary.
Five departing MPs did not receive the payments - one, Rudi Vis, died shortly after the election, three were charged with criminal offences over their expenses and the fifth, Harry Cohen, who was censured over his expenses by Parliament's standards committee, was stripped of the payment as a punishment.
Another former MP caught up in the expenses scandal, Margaret Moran, received half her grant, the spokeswoman said - she had been entitled to £54,403.
All the other former MPs on the list had received their full entitlement, which the Commission spokeswoman said could be worked out using information "in the public domain".
But that was criticised by Heather Brooke, whose Freedom of Information campaign helped bring MPs' expenses claims to light.
She told the BBC it was a "kind of subtle form of secrecy" because most people would not work out the amounts received: "If they know it, why don't they just publish it?"
"They are paid by the public, so why don't they just give the public that information?"
The Taxpayers' Alliance pressure group said taxpayers would be angry to see MPs able to "waltz off with big pay outs" when there was huge pressure on the public finances.
"It's quite unbelievable that it has taken so long for the details on resettlement grants to come out," said campaign director Emma Boon.
"It's not good enough for Parliamentary Authorities to publish a list of names and expect readers to piece together the rest of the information and work out what MPs were entitled to. Resettlement grants are paid for out of taxpayers' pockets, they have a right to see where their money went."
At the 2010 general election, 149 MPs had announced they were standing down ahead of the 2010 election - a post-war record - and a further 76 lost their seats.
Among those in receipt of the grants were Derek Conway, the former Conservative MP who was reprimanded over taxpayer funded payments to his son, Tony McNulty, the former Labour minister who lost his seat and was ordered to repay £13,837 claimed on his second home, where his parents lived.
Others include Douglas Hogg, who submitted an invoice to expenses officials which included the costs of clearing his moat, Margaret Moran - who claimed £22,500 to treat dry rot at a property 90 miles from her constituency, Julie Kirkbride and her husband Andrew MacKay, who each made claims for different "second homes" and Jacqui Smith, whose claims included one submitted by her husband for pornographic films.
The Taxpayer's Alliance, who did their own calculations last year based on 218 MPs claiming the resettlement grant, estimated they would have received £10.4m in total.