A “LEADERS” debate is due to go ahead on STV tonight despite the exclusion of the Scottish Greens.

Protests from the party have failed to change the format which will see SNP First Minister Nicola Sturgeon up against Scottish Labour leader Jim Murphy, Scottish Conservative leader Ruth Davidson and Scottish LibDem leader Willie Rennie at the Assembly Rooms in Edinburgh.

Scottish Greens co-convener Patrick Harvie MSP said the party's omission was “unfair”.

“During the referendum campaign the Scottish Greens played a prominent role, appearing regularly in televised debates and discussions, perhaps most notably at the STV debate at the Assembly Rooms,” he said.

“In the context of a post- referendum election, with a politically engaged electorate and a decline in support for two or three parties, it is clear that a broadcaster not reflecting a broader range of voices will not meet the expectations of its audience.”

However, STV has not backed down over the debate, which is being broadcast live from 8pm to 10pm.

Chaired by STV political editor Bernard Ponsonby, it is likely to attract viewers from outwith Scotland following Sturgeon’s success in last week’s leaders’ debate, where she emerged a clear winner over Labour leader Ed Miliband and Prime Minister David Cameron.

Some will be tuning in to see her defend herself against The Daily Telegraph’s allegations that she told a French diplomat she wants Cameron to remain in Downing Street.

Both Sturgeon and the French diplomat have denied there is any truth to the claims, which were leaked to the Telegraph from the Scotland Office. It is possible that Sturgeon will challenge both the LibDems and the Tories over the matter tonight, as she believes she is the victim of a “dirty tricks” campaign.

She is also likely to reiterate the SNP’s opposition to the renewal of Trident and will maintain there is an alternative to Tory austerity policies.

For Jim Murphy, it will be a chance to assert himself after watching Sturgeon triumph in last week’s debate.

However he is already on the back foot as he has to be careful to maintain Labour policies laid down by Westminster while still appearing to be more than the man in charge of the branch office. He will accuse Sturgeon and the SNP of acting as the Tories’ “little helpers” by targeting Labour seats in Scotland. He will also try to show that Scottish Labour is a still a party of the people by repeating his promise of a £175million fund aimed at “waging war on poverty”.

For their part, the Lib Dems have promised £800m to improve the NHS in Scotland, but whether they can carry this out is debatable as the NHS is a devolved issue and it is up to the Scottish Government to decide how any extra money is spent. Rennie is also likely to have a hard time defending the LibDems’ part in the Coalition Government and their broken promise over tuition fees for students at universities south of the Border.

As a Tory, Davidson has nothing much to lose in tonight’s debate and will gain some respect if she is able to mount a strong defence of her party’s austerity measures against the other leaders, particularly as the Tories have announced plans to cut another £13 billion from the welfare bill.

The debate will be broadcast live on STV and will also be available on the STV player on the broadcaster’s website.