Charities have warned that the Government's lobbying legislation will still curb free speech, despite attempts by ministers to allay their concerns.

The latest blow for Andrew Lansley's proposals comes ahead of scrutiny of the plans by MPs next week.

The Transparency of Lobbying, Third Party Campaigning and Trade Union Administration Bill will return to the Commons on Tuesday as MPs mull changes announced by the Government to address issues raised by charities and campaign groups.

Changes clarify rules on third party political spending, make clear public rallies rather than member-only meetings are to be regulated, and states that campaigners responding to policy questions by the media are not captured by the Bill.

Commons Leader Mr Lansley was "confident" changes met charities' fears.

Advice to the National Council for Voluntary Organisations (NCVO) says it may impact on their activities by bringing campaigning activities in election years in the scope of the proposed spending cap.

Sir Stuart Etherington, NCVO's chief executive, said: "The Government's commitment to address the legitimate concerns of many charities and other voluntary organisations remains welcome, however, the proposed amendments do not go far enough.

"The assurances given by ministers on the floor of the house to ensure that charities will still be able to support specific policies that might also be advocated by political parties have not been met. Legal advice provided to NCVO indicates that the proposed amendments put forward by the Government will mean that much campaigning activity by charities and other voluntary groups will still be covered by this excessively bureaucratic and burdensome regime."