THE Tories have launched an ­orchestrated attack on Scotland's ­charities which could cause fundraising efforts to collapse, the sector's leading figure will warn today.

Martin Sime, chief executive of the Scottish Council for Voluntary Organisations (SCVO), says philanthropists and corporate donors could be put off pledging support because of outspoken criticism by Conservative figures.

He will warn in a speech to the Institute of Fundraising annual conference in Glasgow today of an "orchestrated attempt to muzzle charities".

Mr Sime says the criticism of the work of charities could cause "irreparable damage to the fabric of society".

He believes Tory ­ministers and MPs have co-ordinated the attacks on charities to silence critics of controversial policies such as welfare reform.

He said he was particularly concerned about the impact on philanthropists and corporate donors, who might become wary of outspoken charities, ceasing to fund anything but utterly safe, non-contentious work.

Criticism by Cabinet ministers has come from disgraced former Civic Society Minister Brooks Newmark. Mr Newmark, who recently resigned over a sex scandal, told charities they should "stick to their knitting", rather than become involved in politics.

In June, Chris Mould, who chairs food bank charity the Trussell Trust, said it had toned down criticism of the benefits system after being warned in private conversations with "those in power" that it might be shut down.

Last year Westminster Justice Secretary Chris Grayling told charity leaders they were putting too much emphasis on campaigning and not enough on service delivery.

Backbench Tory MP Conor Burns also reported Oxfam to the Charity Commission for being "overtly political" when it campaigned against food poverty in Britain.

Mr Sime argues undermining trust in charities among the public, corporate donors and philanthropists is counterproductive.

He says: "If such attacks continue they risk undermining public trust in charities which will make it more difficult to raise money for good causes. The daftest thing of all about this attack is that if donors retreat the government will face rising costs."

Mr Sime says it is the job of the organisations he represents to hold ministers to account.

He said: "We represent those who aren't included and don't have a voice. That is utterly non-negotiable.

"Ministers have recently accused us all of being left-wing, anti-business and full of Labour Party activists. This is part of an orchestrated attempt to undermine charity campaigning on behalf of the most marginalised and vulnerable people in our society - the very same people who are bearing the brunt of austerity policies and the politics of division and blame.

"Even the Chancellor has railed against anti-poverty campaigners. Hostile legislation is attempting to limit civil rights and funding is being withdrawn from organisations who criticise government policies."

Charities appear to be on a collision course with the UK Government, he said and this could have severe consequences. He added: "Public generosity is such a vital component to so many good things in public life. Charities raise a lot of money for good causes which would otherwise have to be paid for by government. Undermining trust in charities and what we are trying to achieve is altogether stupid, a daft thing to do."

Charities were not party political and would not tell people who to vote for, but should not be bullied into silence, Mr Sime said. He added that politicians should develop thicker skins. "They should take up other jobs, if they don't like it," he said.

A Cabinet Office spokeswoman said: "Amazing work is going on up and down the country, led by large companies, small grassroots schemes and inspirational individuals. Our role is to help these people and organisations do more."