Ministers must do more to demonstrate they are acting on the recommendations of public inquiries, a new report says.
The National Audit Office said it was "not always clear" to the public whether inquiries were having their intended impact as there was no central body for tracking their progress.
Of the inquiries it examined which had made recommendations since 2005, it estimated 45% of these were accepted.
A third were accepted "in principle" while 7% were rejected.
In the case of the 2012 Leveson report into press standards, the public spending watchdog said there was "no clear response" reported to the public to any of its 92 recommendations.
The government is not legally obliged to accept the recommendations of public inquiries.
The NAO estimates the 26 government-funded inquiries which have concluded since 2005 have cost £239m.
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They ranged in cost from the £24.9m spent on the Al-Sweady inquiry into allegations of unlawful killing and ill treatment of Iraqi nationals by British troops to the £200,000 spent on the Harris Review into self-inflicted deaths in custody of 18 to 24-year-olds.
Their average duration was 40 months, with the Iraq Inquiry into the UK's participation in the 2003 invasion taking twice as long, at 84 months, as every other inquiry bar Al-Sweady.
Of the eight inquiries examined by the NAO which made recommendations - including Leveson, the Mid Staffordshire Inquiry into NHS care failings and the Litvinenko Inquiry into the killing of the ex-Russian spy - it found "readily accessible" information on progress was available in half.
In the others, the watchdog said ministers had given updates to Parliament but not outlined specific details of what action had been taken in response to individual recommendations.
Departments varied in how transparent they were in acting on the findings of reports.
Part of the problem, it concluded, was that there was "no overall oversight across government for monitoring and tracking whether inquiries have achieved their intended impact and whether recommendations, where made, have been implemented".
The watchdog said ministers had not acted on recommendations from MPs on how inquiries were run, such as updating and publishing guidance to inquiry chairs, reviewing the rules on allowing those criticised in reports to comment on extracts and "sharing lessons learned" reports.
But it did find that the Home Office, which has been responsible for instigating six inquiries since 2005, had developed its own "bespoke process" to give inquiry teams more support.
Downing Street has said it is committed to ensuring the lessons of the Iraq Inquiry report are fully "embedded" in the procedures and culture of Whitehall.
It has insisted changes since 2010 mean the cabinet can no longer be "bypassed" as the Chilcot report suggested had happened under Tony Blair.