Tommy Sheridan: I've a reasonable chance of returning to Holyrood

He called on independence supporters to back Solidarity in the regional ballot, claiming list votes for the SNP would be wasted under the Holyrood system because the party was on course to win almost every constituency.

He said nationalists should "punish the Unionist parties" by "minimising" their representation at the Scottish parliament.

Solidarity's flagship pledge, if it wins a seat, is to bring forward an "Indyref 2" Bill that would facilitate a referendum in 2018.

Mr Sheridan predicted victory in the vote, with 60 to 65 per cent of Scots backing Yes, leading to formal separation from the UK on April 6, 2020, the 700th anniversary of the Declaration of Arbroath.

He said Solidarity would give the SNP "a bit of backbone".

Solidarity did not contest last year's Westminster election, choosing instead to endorse the SNP and Nicola Sturgeon's pledge to oppose austerity.

Since then, however, Mr Sheridan said the SNP - which is proposing modest tax cuts for the better off - had abandoned that position.

"We are disappointed as a party that the SNP has, in the last 12 months, not opposed austerity in the manner that their General Election mantra led us to believe

they would.

"We think they need a bit of backbone. We will supply that backbone," he told a handful of supporters gathered in a Glasgow hotel.

He accused the SNP of "complying with austerity" and called for Holyrood to join a "council of war" with local authorities, trade unions and community groups to defy spending cuts.

Solidarity is not backing the SNP by name in the election but wants as many pro-independence MSPs as possible, arguing that leaving the UK is "the road to a socialist Scotland".

He said: "The SNP will romp this election, they will form a majority government on the constituency vote alone.

"We are appealing not just to SNP supporters but those with independence in their hearts.

"We ask you to look at the voting system and declare loud and proud you are using your second vote not to help the Unionist parties but to punish them."

The party is fielding candidates in all eight Holyrood regions.

In addition to Mr Sheridan, hopefuls include his wife, Gail, South Lanarkshire councillor Pat Lee and Kevin Gore, a singer who performed his song Independence Day during the manifesto launch.

Supporters also held a minute's silence to mark International Workers' Memorial Day before hearing from Mr Sheridan.

Among the other policies he outlined, the former MSP pledged to campaign for cannabis to be legalised, saying: "We should not criminalise a section of our community for a victimless crime."

He also spoke out in favour of leaving the "undemocratic and anto-socialist" EU, demanded a ban on fracking and nuclear weapons and said "criminal" public-private contracts to build schools and hospitals should be cancelled.

Solidarity faces competition for regional votes from the independence-supporting Greens and RISE, the left-wing alliance which includes the SSP, the party Mr Sheridan used to lead.

Asked to rate his chances, he claimed the party had a "reasonable chance" of winning seats across Scotland.

He claimed support for Solidarity was at six per cent - around the threshold for gaining a list seat - though opinion polls suggest it is much lower.

Mr Sheridan won a Holyrood seat in 1999 and 2003 as leader of the Scottish Socialist Party.

But he quit as leader in 2004 to sue the News of the World for alleging he was a swinger, a decision that split his party and led to him forming Solidarity.

Although he won his defamation case, he was subsequently jailed for lying under oath.

Former allies insist he is no longer relevant to left-wing politics in Scotland.

The latest poll, from TNS, suggests the Greens are enjoying by far the most success of those parties contesting the election on the regional list. Support for the party is running at eight per cent. The poll found only two per cent of voters planned to support a party outside the existing five Holyrood parties.