NICOLA Sturgeon will need Theresa May’s help to turn her draft referendum bill into reality.

Although the First Minister did not say so, the document published next week for consultation would be tossed out by the Presiding Officer if she tried to lodge it at Holyrood.

That is because the bill, essentially a warmed over version of the Scottish Independence Referendum Act 2013, is not legislatively sound as it stands; something is missing.

Read more: Nicola Sturgeon warns Theresa May - I'm not bluffing about independence vote

That vital ingredient is Westminster’s consent, specifically a “Section 30 Order” temporarily devolving powers to Scotland for a legally watertight referendum.

This is what David Cameron granted as part of the Edinburgh Agreement he and Alex Salmond signed in 2012, clearing the way for the referendum two years later.

As a co-signatory to that same agreement, Ms Sturgeon knows this full well.

In theory, she could, as Mr Salmond once contemplated, hold a “consultative referendum” without Westminster’s consent, but that would certainly end in a tangled, time-wasting legal battle. With the Brexit clock ticking, that is time she doesn’t have. But why should Mrs May oblige? When her predecessor agreed to the last referendum, support for independence was at 27 per cent and a Yes vote seemed thoroughly far-fetched. Now support for Yes is a few points shy of 50 per cent, and the Union is on a shaky peg.

Read more: Nicola Sturgeon warns Theresa May - I'm not bluffing about independence vote

However, as Scottish Tory leader Ruth Davidson pointed out last month, refusing a Section 30 Order would hand the SNP a new Westminster outrage and boost the case for independence. “It would play directly into the Nationalists’ hands,” she said, adding: “It was wrong for the Spanish government to say that they were going to block a Catalan referendum. You saw what happened there, the way people got on to the streets of Barcelona.” The draft referendum bill is a political taunt. Ms Sturgeon is daring Mrs May to shoot it down.

But it is more than gamesmanship. When the bill was first outlined in Ms Sturgeon’s programme for government last month, officials said it would be published by mid-2017. The First Minister could have waited almost a year, instead she has moved within weeks, capitalising on the backlash to the Tories morphing into Ukip at their conference.

It may not be ready to enter Parliament, it may not (yet) have Westminster’s underpinning, but make no mistake – the draft bill is a very big and tangible step towards another referendum.