The Labour-dominated Select Committee on Administration urged the Home Secretary, Jack Straw, to think again about key elements of his proposals before putting a Bill before Parliament in the new session starting next week.
Although the MPs welcomed the Government's recent concessions to its critics on the issue, they insisted it had not gone far enough. If ministers refuse to give further ground, the changes demanded by the committee are likely to form the basis of amendments to the Bill during its passage through Parliament.
With many Labour MPs committed to a tough freedom of information law, the Government would risk a defeat if it fails to back down.
Yesterday's report said: "We are disappointed that the Government has not amended the basic structure and scheme of the draft Bill." The MPs regretted that, under Mr Straw's plans, there would be "no clear presumption in favour of disclosure" of information. They were worried that the commissioner to be appointed to oversee the new law would not be able to order the release of information, even if he felt this would be in the public interest. Such decisions would continue to be taken by ministers.
The committee warned that the Government's plans would allow "blanket restrictions" on certain types of information, such as the formulation of government policy and the operation of ministers' private offices.
Ministers want material to be kept secret when disclosure would result in "prejudice". But the MPs said this would be "too weak" to ensure much disclosure, and want the test to be changed to "substantial" or "significant" prejudice.
They said the exemptions in the draft Bill remained "too broad", particularly those covering government decision-making and policy formulation and information about commercial interests. "As a result, the amount of information that will become available will be relatively small," they warned.
Although some "particularly objectionable" restrictions had been dropped from theoriginal proposals, the MPs said this still left "fundamental issues on which the Government's position differs sharply from that of the committee".