Ministers moved yesterday to drop even more parts of flagship legislation on child protection in order to avoid an embarrassing failure of the bill.

The move came on the day The Herald revealed Robert Brown, Deputy Education Minister and the man pushing through the bill, had agreed to ditch the third section of the legislation.

The Protection of Vulnerable Groups (Scotland) Bill, was introduced in response to the 2004 Soham murders, with the aim of tightening up the vetting of those working with children and vulnerable adults. While the main principle has been backed by politicians, teachers and charities, the cost and practicality of the measures have attracted almost universal criticism.

The bill would have resulted in one million people, a quarter of the adult population, being subjected to a police background check if their job or voluntary work brings them into contact with children or vulnerable adults.

However, facing widespread dissent from the Liberal Democrat half of the coalition and a damning report from the Holyrood Education Committee, Mr Brown has now dropped the retrospective element of the vetting - a move which means only new staff will be checked until the legislation has bedded down.

Charities and teachers groups say the bill, by focusing on stranger danger, distracts from the more prevalent problem of domestic child abuse. There have also been warnings it will create a vast, expensive bureaucracy and deter people from volunteering.

Last year, Holyrood's Education Committee was told by a host of experts that it should be shelved pending a radical rethink. Mr Brown, a LibDem, is still pushing for the legislation to go through in this parliamentary session. However, Transport Minister Tavish Scott and Deputy Finance Minister George Lyon are believed to be deeply opposed to it in its current form.

The LibDem group has said only "major changes" would allow them to back the Bill, according to sources.

The committee has intimated that the bill cannot move to stage two until the full details of how it will work have been provided. If the bill is further delayed it is unlikely to be completed before the March 28 deadline in the run-up to the May election and would have to be dropped.

MSPs said they would rather see such an important piece of legislation done properly than rushed through.

The voluntary sector believes the legislation would cost them more than £20m in disclosure checking.

Gavin Yates, a spokesman for the Scottish Council for Voluntary Organisations, said: "We cannot have a situation where voluntary organisations are being asked to endorse a system they don't know how much will cost, how it will work and one which would cost us millions to implement.

"We hope the minister will make an announcement that addresses our concerns in the parliament on Wednesday."

An executive spokeswoman said: "The executive is fully committed to making the implementation of the bill successful and has engaged extensively with the full spectrum of stakeholder interests thus far and will continue to do so.

"We recognise retrospective checking has been an issue causing concern. The executive agreed to explore further whether legislative provision relating to the phased introduction of the workforce to the scheme could be subject to separate regulatory provision."

Stage one of the bill will be debated on Wednesday.