Matthew D'Ancona: Sturgeon the tartan prefect can't resist taking centre-stage

On Monday evening, David Cameron hosted a party for Conservative MPs in the garden of No 10: their roars of approval as he spoke echoed around Downing Street.

At No 11, meanwhile, George Osborne awaited a call from Euclid Tsakalotos, the Greek finance minister — by coincidence a fellow alumnus of St Paul’s School. The sense of a party restored fully to power was, according to those present, richly palpable.

Yet power can never be taken for granted. Since their unexpected victory on May 7, the Prime Minister and Chancellor have behaved with conscious discipline, insisting to colleagues that collective celebration must not, under any circumstances, become tribal hubris. They are wise to do so. Barely 12 hours after Tory MPs had cheered Cameron in the evening sun, Nicola Sturgeon was on the BBC’s Today programme declaring the intention of the SNP’s 56 MPs to vote against the Government’s amendment of the hunting ban in England and Wales.

Her chirpy U-turn reminded me of the moment in Trainspotting when Begbie throws a glass off a balcony, launching a huge pub brawl. “The problem is, he’s a mate n aw,” muses Renton, the narrator. “What kin ye dae?” What, indeed? Ms Sturgeon sounded so calm and genial as she spoke — but there was no doubt that her actions were going to cause mayhem.

In February she did indeed declare that “the SNP has a long-standing position of not voting on matters that purely affect England — such as fox-hunting south of the border, for example — and we stand by that”. But her position has changed, not least because of the alleged clamour in England for her party to make good its promise to forge “progressive alliances”. She also feels that Cameron has treated the SNP’s new bloc in Westminster with insufficient respect. Here, then, was an opportunity to “remind the Government how slender their majority is”. And over the balcony went the glass — tossed by a politician who is not even an MP.

This was the most openly retaliatory Commons tactic since August 2012 when Nick Clegg withdrew Lib-Dem support from the new parliamentary constituency boundaries as payback for the Tories’ sabotage of Lords reform. Sturgeon’s intervention has killed off the vote that was due to be held today, marking an unwelcome hat-trick for Cameron. Less than three months into its term of office, the Government has already been compelled by parliamentary arithmetic to postpone proposals to scrap the Human Rights Act and a plan to enact the principle of “English votes for English laws” (EVEL).

In an emergency Commons debate last week, Ed Miliband condemned the current EVEL blueprint as “constitutional vandalism”, quoting Gladstone’s remarks in 1893 when he abandoned his Second Home Rule Bill: “It passed the wit of man to frame any distinct, thoroughgoing, universal severance between the one class of subject and the other.” How, the former Labour leader asked, could an “English law” be identified with sufficient certainty to exclude non-English MPs from the legislative process?

This is a fair question, actually. So interdependent are the constituent parts of this United Kingdom that fewer exclusively English votes may be certified under an EVEL system than might at first seem likely. But the SNP goes much further. In May, Scottish voters elected Ms Sturgeon’s party in all but three of Scotland’s Westminster seats. But the UK electorate comprehensively rejected the Labour-SNP “progressive alliance” that she had championed, choosing instead a Conservative government that is pressing ahead not only with its austerity strategy but an audacious plan to redefine social justice with welfare reform and a National Living Wage.

Yet the SNP leader behaves as though the virtue of her position gives her a special moral mandate. Mhairi Black, the 20-year-old Scottish Nationalist MP for Paisley and Renfrewshire South, has quite rightly been applauded for the rhetorical power of her maiden speech this week. But the content of her remarks was party cant, echoing Sturgeon’s dubious notion that the SNP has an ethical duty to wreck Cameron’s plans and to save the English from themselves. “I reach out a genuine hand of friendship that I can only hope will be taken,” said Black. “Let us come together. Let us be that opposition.”

To which the English are entitled to reply: we thought you wanted independence, not the task of tartan prefects. Such, however, is the lure to politicians of the moral high ground. What they tend to miss are the booby traps and landmines with which this lethal political terrain is encircled.