A union boss has urged Nicola Sturgeon to allow councils to raise tax to "lift the cloud of austerity" from Scotland and stop "hiding behind procedural niceties" in her opposition to trade union reforms.

Unite general secretary Len McCluskey met the First Minister for the first time at the union's inaugural Scottish policy conference in Clydebank on Sunday.

In his speech to conference, he called on Ms Sturgeon to end the SNP's council tax freeze and block the Trade Union Bill.

The Scottish Government said the council tax freeze helped families through the economic downturn and that they have given councils more than enough money to compensate.

Holyrood presiding officer Tricia Marwick, a former SNP MSP, has said Holyrood does not have the power to veto the Trade Union Bill in Scotland, but Labour insists a legally binding veto can be found which does not breach the terms of the Scotland Act.

Mr McCluskey also reminded Scottish unite delegates - who have voted overwhelmingly for the SNP - that Unite remains a Labour-supporting union.

He said Jeremy Corbyn is Labour's best hope for winning back Scottish voters, and said Unite's five-year political strategy within Labour played "no small part" in his election.

On Saturday, Mr McCluskey told journalists that 65% of the union's 150,000 members voted SNP at the general election.

In his speech on Sunday, he told delegates: "I may not agree with that choice, but I can understand it. In some cases, it is a vote that comes from a settled belief that Scotland should be an independent nation-state.

"And in others it is a cry of frustration at the failures of Labour in Scotland over a generation, and a recognition that the SNP have stolen some of Labour's social-democratic clothes.

"For Unite, we are happy to work with an SNP government that appears to value trade unions, to pay more than lip service to social justice and community cohesion, and to share many of our values on other issues as well.

"Nicola Sturgeon and her team have reached out to trade unions - including on vital issues like blacklisting - and we would be letting our members down if we responded anything other than enthusiastically."

But he said the union "can and should demand more from the SNP".

"Nicola's government should not be hiding behind procedural niceties in relation to the Trade Union Bill," he said.

"I'll be saying to Nicola: don't just oppose this wretched Bill, but block it in Scotland.

"And while you're at it, end the council tax freeze and really go the extra mile to lift the cloud of austerity from the lives of the people of Scotland.

"Whatever the SNP does or doesn't do in Edinburgh or Westminster, Unite remains a Labour union, here in Scotland as across all of Britain. Sometimes that is not an easy place to be.

"I understand that many Scottish working people, particularly perhaps the young, feel betrayed and let down by the New Labour years, by a party which had grown bureaucratic and remote from people's needs and, still more importantly, their hopes and visions for the future.

"New Labour let us all down - the illegal wars, the creeping privatisation, the widening inequality, the failure to support manufacturing jobs, the indifference to anti-union legislation.

"All this is the opposite of everything we believe in and looked to Labour to represent, in England and Wales as much as here in Scotland.

"But let's acknowledge something else - Labour's future looks a lot brighter than its past and, to be honest, far more exciting than any of us would have believed possible.

"Under Jeremy Corbyn, Labour is turning a corner. It is rediscovering its radicalism. Reaching out to those it has abandoned, or who drifted away in disappointment years ago.

"In no small part this is thanks to the support our union has given to him, and to the political strategy we have followed inside Labour for the last five years."

Ms Sturgeon said the Trade Union Bill "will be opposed at every single turn" by the SNP.

She said: "Let me say directly to David Cameron today: if the Tories have any respect whatsoever for the democratic process in Scotland they will drop this Bill and they will drop it now.

"It's a measure that I don't think would have ever been proposed, let alone passed, in the Scottish Parliament which why I believe so strongly that the powers over trade union and employment law shouldn't lie with the Tories at Westminster, these powers should lie with our own democratically elected parliament here in Scotland."

She added: "Let me be clear about this: if this Bill becomes law we will not willingly or voluntarily cooperate with it or implement it.

"The Scottish Government, for as long as I lead it, will never ever employ agency workers to undermine strikes.

"The Bill represents a view of the world that sees trade unions as enemies."