A CIVIL war within Scotland's dominant political party dramatically re-opened last night, after SNP bosses moved to strike down a grassroots bid to force through a ban on fracking.

At least 20 party branches had put forward a motion calling for a complete ban on unconventional oil and gas extraction to be debated at its upcoming Spring conference.

However, it has emerged that a powerful party committee that decides the agenda had blocked the move.

Had the motion been debated and agreed, it would have heaped intense pressure on the party leadership to go further than current moratoriums on fracking and underground coal gasification with SNP members technically able to decide party policy.

It follows a fractious debate at the party's last conference in October, when members narrowly backed a motion that had been watered down by the party leadership and stopped short of calling for an outright ban.

Almost half of delegates voted against the motion, which backed the Scottish Government's moratorium, on the basis that it did not go far enough.

However, the party leadership has consistently refused to rule out allowing fracking, insisting it will be led by evidence ahead of taking a decision in 2017. John Swinney has called for fracking revenues to be assigned to the Scottish Government with the matter currently under discussion in talks over the Fiscal Framework with the Treasury.

It is understood that the motion had been put forward by the Edinburgh Eastern branch, and was backed by SMAUG, an internal SNP pressure group that is overtly calling for an outright ban.

Some SNP members fear that prevarication on the issue of unconventional oil and gas could see the SNP haemorrhage support to the Greens at May's Holyrood elections.

Partick Harvie, the Green co-convenor, said: "I welcome the commitment that has been shown by many SNP activists to secure protection for Scotland’s communities against dangerous and unnecessary developments by the extremists of the fossil fuel industry. It must be deeply frustrating for them to be up against a party leadership that’s unwilling to offer voters any clarity on this issue, or even to allow a democratic vote."

Dr Richard Dixon, Friends of the Earth Scotland Director, said: "It is disgraceful that the SNP have rigged the agenda of the spring conference to avoid a debate that would embarrass the leadership. Judging by the mood in the room last autumn there is little doubt that had the motion made it onto the spring agenda the party would vote for a full ban."

An SNP spokesman said fracking was discussed at the SNP conference three months ago, and claimed a position was agreed. He added: "We don't hold another debate on the same subject at each conference."