Michael Geist notes that the UK government appears to be unhappy with the lack of transparency in ACTA negotiations
"More broadly with respect to ACTA the UK considers that transparency is crucial to ensure the legitimacy of the agreement and to stop the spread of rumours. We believe the lack of transparency is unhelpful and do not believe that it is in the public interest."
Of course, the folks pushing for ACTA have no concern, at all, about "the public interest." Their only concern, all along, has been about further protecting their business models. The public interest might go against that, hence their opposition to such transparency.