The Public Accounts Committee highlighted the way some firms seconded staff to the Treasury to advise on technical issues in the drafting of legislation - only for the individuals concerned to return to advise clients on how to use those laws to avoid tax.
Through their work in advising government on changes to legislation they have a detailed knowledge of UK tax law, and the insight to identify loopholes in new legislation quickly.
We have seen what look like cases of poacher, turned gamekeeper, turned poacher again, whereby individuals who advise government go back to their firms and advise their clients on how they can use those laws to reduce the amount of tax they pay.
More top news
David Cameron will be facing a hostile audience when he meets with leaders from the remaining 27 EU nations this week, writes James Mates.
Baroness Warsi warns reports of hate crimes are rising after a "divisive" EU campaign largely focusing on immigration spurred street abuse.
Labour has descended into crisis as several high-profile members of the shadow cabinet have quit in the past few hours. Here's who they are.