Businesses privately lobbying government to water down green regulations are at growing risk of their activities being uncovered, after Friends of the Earth secured a major legal victory in its campaign to impose greater transparency upon corporate lobbyists.

The information tribunal ruled last week that the Department for Business, Enterprise and Regulatory Reform (BERR) must release full details of meetings from 2005 between former business secretary Alan Johnson and former head of the CBI Digby Jones.

Friends of the Earth said that the meetings included "frank exchanges" over a range of environmental and legislative issues, as well as details of an "away day" involving senior Whitehall and CBI officials. The green group argued that the documents were in the public interest and should be released under the Freedom of Information Act.

The latest ruling largely upholds a decision last year from information commissioner, Richard Thomas, who said that the bulk of the documents should be released. However, BERR mounted an appeal against that decision, claiming that the release of some of the material requested would damage policy making within government.

The tribunal rejected this line of argument and ordered the government to release the bulk of the material within 28 days, although it agreed with the department that some of the documents should remain confidential.

A BERR spokesman said that the department maintains that "there are circumstances where it is in the public interest to protect the 'thinking space' necessary for good public policy formulation and to enable the Department to have a private discourse with external organisations". He added that it would consider the judgement and reach a decision over whether or not to appeal the decision to the high court within 28 days.

A spokeswoman for Friends of the Earth said that a version of the documents seen by the green group featuring large blacked out sections, suggests that the series of meetings contained "frank exchanges" over a range of environmental issues.

Phil Michaels, head of legal at Friends of the Earth, said that it was unclear if the documents had the potential to cause the government or the CBI any embarrassment, but added that BERR had gone to a great degree of effort to keep minutes from the "away day" meeting private. "We know that meeting happened soon after the election and was wide ranging, covering issues such as planning reform, climate change and nuclear policy," he said.

The green group is reluctant to claim that the information tribunal decision sets a precedent for future Freedom of Information requests, but it does highlight the growing pressure on business lobbyists to be more transparent in their activities.

"There are more and more lobbying transparency cases about and we see this decision as a step in the right direction," said the Friends of the Earth spokeswoman. "Firms need to be aware that even four years after the event, these types of lobbying activities can become public."