Government proposals for a statutory register of lobbyists will do little to improve transparency and may cover less than 1% of ministerial meetings, an MPs' report said.
The report called on ministers to ditch their plan for a register covering only lobbyists working on behalf of third parties, and to instead introduce regulation to cover all those who lobby professionally.
New regulation should cover not only third-party lobbyists but also those working in-house for companies, charities, trade unions and think-tanks, said the report by the House of Commons Political and Constitutional Reform Committee.
Before becoming Prime Minister, David Cameron identified lobbying as "the next big scandal waiting to happen" and promised to introduce measures to curb abuses.
The coalition agreement of 2010 promised a statutory register of lobbyists to ensure greater transparency.
But proposals published in January this year envisaged that the register should carry details only of "those who undertake lobbying activities on behalf of a third party client or whose employees conduct lobbying activities on behalf of a third party client".
The cross-party committee said this would mean a "one-man band" lobbyist would be required to register, name his clients and pay for the privilege, while those working directly for large companies would not have to sign up.
The MPs said they had seen "no evidence to suggest that third party lobbyists are a particular problem within the lobbying community - indeed the Government's own records of ministerial meetings suggest that third party lobbyists make up less than 1% of all meetings with ministers".
And they added: "The proposals single out third party lobbyists in an attempt to create a narrow focus for a register that will meet a coalition pledge, but do little to improve transparency about lobbying. The committee recommends that the Government scraps its plans to introduce a statutory register of third party lobbyists, and instead introduce regulation to cover all those who lobby professionally, in a paid role, including those who lobby on behalf of charities, trade unions, and think-tanks."
A Cabinet Office spokesman said the Government would provide a detailed response to the report "in due course", but added: "Lobbying has an important role in the policy-making process, ensuring that ministers and senior officials hear a full range of views from those who will be affected by Government decisions. But it must be conducted in a transparent and open way."