THE SNP last night raised the prospect of a second referendum, demanding that Holyrood should have the power to call one whenever it wants without Westminster’s permission.

The party has tabled an amendment to the Scotland Bill, which enters its final stage in the Commons tomorrow, which would give MSPs in Holyrood complete control over the issue.

Although Holyrood decided the timing and some of the rules of the last referendum, it was only able to do so because Westminster temporarily bestowed the relevant powers.

However, the “Section 30 order” granted by David Cameron to empower MSPs also dictated the referendum had to be held by December 31 2014, and had to use a single ballot paper offering voters only two choices, thereby excluding a Devo Max option.

Under the new amendment tabled by SNP Westminster leader Angus Robertson, Alex Salmond and four other SNP MPs, all such conditions would be removed, giving Holyrood unfettered control of all aspects of another referendum.

“This new clause would permit the Scottish Parliament to decide whether and when to hold a referendum on Scottish independence,” the MPs explains in an accompanying note.

First Minister Nicola Sturgeon has said she would only hold another independence referendum if there was sustained public appetite for one, and suggested a UK vote to leave the EU despite Scotland wishing to remain could be the trigger.

However, David Cameron has declared the issue “settled for a generation”, suggesting he may not concede the power to hold a fresh plebiscite.

Pete Wishart, the shadow leader of the house and one of the movers of the SNP amendment, told the Sunday Herald: “It’s in response to all the conversations going on about a second referendum, how that could be triggered and who has responsibility.

“This is a power that should rest with the Scottish people and if they decided the moment and the conditions were right, that would be a matter for Scotland and the elected representatives of the Scottish people, not Westminster. That call should be made by Scotland.”

Robertson added: “Whether or not Scotland has a referendum in the future should be up to the people - and in the hands of the Scottish Parliament - rather than the UK government.”

It is now down to the Commons Speaker to decide whether the amendment is called.

More than 200 amendments have been tabled to the Bill, yet just five hours have been set aside for Monday’s debate - a timetable Wishart described as “ridiculous”.

He insisted the referendum amendment was intended "seriously" and not simply for show.

Scottish LibDem leader Willie Rennie said the SNP had “a one track mind”.

He said: “With their every waking moment they are planning for another referendum and the tabling of this amendment confirms that.

“Nicola Sturgeon tells us in public that she respects the result of the last referendum but her representatives in Westminster are quietly plotting to disrespect the result."

The Scotland Bill is designed to translate the recent Smith Commission on more devolution into reality, and so deliver the pre-referendum “Vow” made by the three Unionist parties.

The SNP has also tabled an amendment to devolve equalities legislation to Holyrood, which it claims could make Scotland a “world leader” on the issue.

As it stands, the Scotland Bill would only devolve the power to set gender quotas for the boards of public bodies, but the SNP is seeking full control of equalities law - a move last night backed by a range of campaigners for disability, LBGTI and ethnic minority rights.

Despite the idea being rejected by MPs in June, the SNP has also tabled an amendment to give Holyrood full tax and spending powers, known as full fiscal autonomy.

Deputy SNP leader Stewart Hosie said “the final say” on whether the Scotland Bill became law rested with the Scottish Parliament, which must give its formal approval.

And he warned that would depend on a “satisfactory agreement” on a fiscal framework - the rules and institutions which will govern future Scottish tax and spending.

Salmond will give evidence to the House of Lords Economic Affairs Committee on the devolution of public finances, including the fiscal framework, on Tuesday.