The MPs' expenses watchdog has been allowing politicians who break rules to fix issues and repay money in secret.
The Independent Parliamentary Standards Authority's (Ipsa) compliance officer Peter Davis has been settling almost all his cases without any publicity - despite promising to disclose the outcome of all investigations.
The approach - laid bare in a response to a Freedom of Information (FOI) request - emerged after Mr Davis was criticised for failing to announce that claims by three MPs had been referred to police last year.
The watchdog, who operates separately from Ipsa, was previously forced to back down when he proposed conducting probes in secret to prevent "reputational damage" to MPs.
But new details of his casework suggests he has been avoiding disclosure by staging in-depth "assessments" of complaints, during which politicians can hand back money or resolve issues without facing formal "investigations".
Some 40 "assessments" were undertaken in 2014-15, but just one - relating to Tory Bob Blackman's mileage claims - became a formal investigation and was therefore revealed publicly.
Among the cases listed as "closed prior to an investigation" was one in June last year where an unnamed MP claimed for a taxi journey that was not allowable.
The compliance office concluded it was a "legitimate error by a member of staff" and there was no need for any action because it had been "repaid in full by the MP".
In another case, an allegation was made that an MP's staff had filed duplicate claims for a hotel. Mr Davis dropped the matter at assessment stage after "the MP provided a valid explanation for why two separate hotels were claimed inadvertently for the same night and (...) repaid".
Other MPs were permitted to avoid publicity about using taxpayer-funded websites for party-political material by paying back website domain fees to Ipsa, or simply removing content from sites.
Many of the "assessments" appear to have gone into significant detail before being dropped.
A complaint about excessive toner ink and first class travel claims was dropped after "analysis of information provided by complainant and Ipsa showed no evidence of a scheme breach".
Another in October last year into whether an MP's claims for advertising had gone on "party political campaigning" was closed because "it was judged, on balance, that the adverts did not constitute campaign expenditure".
The FOI disclosure shows "allegations of a criminal nature" were made by Ipsa about the "staffing costs" of two unnamed MPs on February 4 and February 24. They were apparently referred to police the following month.
Former MP George Galloway was subject to complaints in January and March that his Commons staff were "engaged in non-parliamentary work during contracted hours".
Those allegations were both referred to Scotland Yard - but apparently not until March, and again without Mr Davis opening a formal investigation that would have required public disclosure.
In August 2013 an MP's staff member alleged that some employees of a politician were engaged in non-parliamentary work during contracted hours.
This probe was later suspended due to "ongoing criminal proceedings related to the complainant". It is not clear whether it has since been dropped or resumed.
Bowing to a wave of criticism over the proposals for secret investigations into MPs last December, Ipsa chairman Sir Ian Kennedy insisted the organisation was committed to being "transparent" and would "continue" to name MPs under investigation.
But the approach taken by Mr Davis suggests the regime is significantly less transparent than that operated by the House of Commons.
The identities of MPs referred to the police at the request of the parliamentary standards commissioner Kathryn Hudson have been announced publicly.
Ms Hudson also publishes details of cases that are "rectified" with small repayments, changes, or apologies, and information about complaints that are not upheld.
Mr Davis, a former senior police officer, had not revealed the fact that MPs had been referred to the police before it was mentioned in three paragraphs on page 74 of his 77-page annual report last week.
In the report, he defended his approach to publicity, stressing that he would do as required and no more.
He said: "I am cognisant that publicity, especially in cases without foundation, carries an inherent risk of reputational damage."
He said the procedures governing his role set out the "information I am required to publish with respect to an investigation, and when this should take place". He said: "I will not deviate from this."
In evidence to the Standards Committee in October last year, Mr Davis said: "I can see that the vast majority of cases can be dealt with quite effectively without the need for any publicity."
Jonathan Isaby, chief executive of the TaxPayers' Alliance, said: "It's crucial that these cases are handled properly but taxpayers will expect transparency too, so that both MPs and Ipsa can be held to account.
"Ipsa must have processes in place to ensure that MPs are getting the appropriate support to enable them to do their job while maintaining public trust in the system. For that to happen, the authorities themselves must be open to public scrutiny."