Internet marketing firm Phorm neglected to mention to the Home Office that it had conducted secret software trials on BT users.
Such is the claim of the Register, which suggests that the firm held a meeting with Home Office officials in August last year in which it did not disclose the fact that it had completed two product tests on unwitting BT customers.
Phorm and BT have both attracted criticism for failing to inform customers that they would be subjected to the trials.
Some commentators have suggested that doing so was illegal.
The Home Office announcement was made following a request made under the Freedom of Information Act.
However, Phorm rejected the claim in a statement, saying: "We have been entirely open on our consultations with stakeholders across the industry and that part of this process included a meeting, at our request, with the Home Office."
BT has declined to comment on the legality of the trials.