THE noisy walk-out staged by SNP MPs in the Commons on Wednesday marked the start of a new obstructionist phase for the party, we’re told.

Filibusters and obscure parliamentary devices to disrupt Westminster business and delay Brexit legislation are afoot.

The cosy days are over, and the Nats are about to cut up rough.

Well, possibly. You can be sure Speaker Bercow is already swotting up on possible “guerilla tactics”, and what he can do about them.

The walk-out succeeded in drawing attention to the ‘power grab’ in the EU Withdrawal Bill and the pathetic 19 minutes of pseudo-debate given over to its devolved aspects the previous day.

But the law of diminishing returns risks any obstructionist looking juvenile and tiresome after a while. Voters also tend to prefer hard-working MPs over jesters.

To me, the walk-out also marked the start of the 2021 Holyrood election campaign, and the launch of the SNP’s theme, one that Brexit has given real traction: ‘Devolution is dead, long live independence’.

Right now, that might sound a bit fanciful. Devolution is plainly not dead, even if it’s been in better health. But there are almost three years to the election, and I suspect the SNP will be using them all to bang home that it’s on its last legs.

As the party found in 2014, the Union is a tough target. It has 300 years of history behind it. It is self-evidently durable. Many voters are vehemently attached to it.

But devolution is a softer affair. People are glad its here, sure enough, but are they brimming with passion about it? Are campaigners knocking doors on a wet Tuesday night for it?

Far better, therefore, to stop railing against the Union and start regretting the failure of devolution.

Despite resisting it, the SNP won’t condemn devolution. Rather, they may reflect it has been a worthy experiment. But, alas, an experiment that after 20 years has plainly run its course. Hence the need to vote for something new with a bit of life in it.

Nicola Sturgeon knows she can’t extract a referendum from a DUP-reliant Theresa May in this parliament. She also needs time to refresh the case for independence.

She knows the middle way of ‘more powers’ was popular in 2014. But if that option was taken out the equation because, as you’ll hear ad nauseam, devolution really isn’t working anymore, in a polarised choice between post-Brexit Tory Westminster and independence, then independence has a shot.

So come 2021 she’ll ask voters to give the SNP an irresistible mandate for that referendum and to give devolution a decent burial.

In this endeavour, Brexit is her friend. It may not have given the SNP the boost it expected after the EU referendum, but it is still early days. Besides the economic pain, lack of a plan, Tory infighting and Westminster chaos, it has also exposed the limits of devolution.

It is Nat 1.01 that Westminster is sovereign and can impose law on Scotland, regardless of Holyrood’s wishes. That has always been the case. But theory is one thing, practice another. Brexit has opened a lot of eyes. Suddenly, people can see the electrified fence and the sign on it saying 'thus far and no further'.

There was a lot of campaign hype about Westminster pressing ahead with the EU Withdrawal Bill against Holyrood’s wishes on Tuesday.

Ms Sturgeon was wrong to say the Tories had “ripped up” the Sewel convention, which says Westminster will “not normally” legislate in devolved areas without Holyrood’s consent. It does not say “never”.

It was also mince for SNP Westminster leader Ian Blackford to claim one example in 20 years had turned “Sewel on its head”.

However both were right to say it was unprecedented, and both were right to call out the insult of the UK government ramming it through.

That played straight into the SNP narrative that the Tories never wanted devolution, and are now killing it by neglect if not by design. Scottish Secretary David Mundell stressed it was not “a new normal”.

But the SNP now plans to play hardball with other Brexit-related legislation and it may well become the new normal. There are likely to be more Holyrood refusals, more confrontations, more departures from the Sewel convention. The UK government is on a fixed schedule. Even if it had the inclination to bargain, it doesn’t have the time.

The SNP know it, and so plan to position Holyrood in front of the Brexit juggernaut and let it get run over for the cameras.

Critics will call it breaking the system in order to complain the system is broken, others will say it is resisting rotten legislation and exposing the confines of devolution.

Ms Sturgeon’s strategy might pay off. I wouldn’t discount it.

But it won’t be easy. She could come a cropper in an early general election. Voters might turn against SNP MPs who don’t appear serious about Westminster. A Labour win would rob her of a Tory bogeyman on which to pin devolution’s end.

Making 2021 about a second referendum also writes the sales pitch for her opponents. They will run a ‘Sack Sturgeon’ campaign, urging voters to bin the FM and settle the independence question.

On paper, there is no election of any kind in Scotland this year, or next year or in 2020. But don’t relax too soon. The great three-year campaign is already upon us.