The inquiry's report is troubling. It records that Thompson and Clark positions itself as expert in "issue motivated groups", by which it means environmental, animal rights, peace campaigners and the like.
But the most disturbing targets were the insurance claimants whose meetings were monitored and sometimes secretly recorded to assess threats to the safety of staff of Southern Response.
The inquiry finds that even after the insurer took steps to protect its staff and train them to deal with angry claimants, it continued to use Thompson and Clark to monitor them for the sake of its "corporate reputation". The spies attended and recorded several meetings, including two led by lawyers discussing legal options and strategy.
The State Services Commission's code of conduct for government agencies using private investigators requires impartiality to be upheld.
The inquiry finds MBIE failed in this respect when Thompson and Clark, acting for the oil and gas industry, was able to "embed itself as a crucial participant within the regulatory and enforcement function" of the ministry under the Crown Minerals Act.
Among those Thompson and Clark calls "issue motivated groups" are Safe (Save Animals from Exploitation), Farmwatch, The Green Party, the Mana Movement, Greenpeace and some iwi groups.
The report is rightly concerned that labelling these groups in this way can undermine legitimate peaceful protest and inhibit constructive relationships between them and the government.
The law on surveillance sets boundaries that should be broken only by state agents with a judicial warrant.
For everybody else, including private security consultants, it can be an offence to secretly record private communications, trespass on private property or intrude in situations where people have a reasonable expectation of privacy.
If private investigators respect those boundaries, everybody's liberties should be safer.