Today marks 250 years since the birth of the radical Scottish political reformer Thomas Muir.

The adjective “radical”, of course, has to be placed in context. What Muir demanded in the late 18th century was universal suffrage, de rigour now but back then the cornerstone of radicalism across the British Isles.

Muir paid heavily for that aspiration. Charged – along with the other “Scottish Martyrs” – on trumped up charges of sedition, he was exiled to an Australian penal colony but escaped en route and saw out his days in France.

Twenty-first century politicians like invoking figures like Muir, not least because of his electric oratory. “From my infancy to this moment, I have devoted myself to the cause of the people,” he stormed at his trial. “It is a good cause. It will ultimately prevail. It will finally triumph.”

Tonight at St Mary’s Cathedral in Edinburgh (the Anglican one, the Capital has two) Alex Salmond will no doubt quote these words as he delivers the first Thomas Muir Memorial Lecture, an event organised by the superb Word Power Books and supported by the Friends of Thomas Muir.

Anyone who’s familiar with the life and career of the former First Minister will be aware that he likes identifying with radicals, particularly those from Scotland’s history. As well he should, for independence – however qualified – has always been a “radical” constitutional aim.

Beyond that, however, Mr Salmond shares the very contemporary trait of seeking to claim a “radical” mantle while advocating pretty orthodox, centrist policies. Other words are used, for example “progressive”, a tradition that at various points since 2005 every major Westminster party (and I include the SNP) has laid claim to.

And in the peculiar circumstances thrown up by the post-referendum, post-general election world UK politicians are busily trying to out-radical one another. With the rise of Nicola Sturgeon and, more recently, of Jeremy Corbyn, those on the left have convinced themselves that rhetorical radicalism is a necessary component of modern electoral success.

Take, for example, the newly elected Scottish Labour leader Kezia Dugdale. “Power,” she said a few days ago, “means that left-wing posturing will have to be replaced by socialist policy.” Now by “socialist policy” Ms Dugdale meant little more than the fairly mainstream proposal to increase the upper rate of income tax to 50p in the pound, a move that would raise only a modest amount of additional revenue.

But that’s not the point, for after decades of consensus (on the left and right) that income tax ought to be as low as possible, advocating a tax increase (even a relatively meaningless one) has the desired effect of appearing “radical”. Indeed Ms Dugdale deployed hyperbole by referring to her idea as “radical redistribution”, when in fact it would merely return the upper rate to pre-2012 levels.

The new Scottish Labour leader also clearly feels under pressure from her own party, with most centre-left commentators now accepting that Jeremy Corbyn – the closest the UK has come to a genuinely “radical” politician in the last couple of decades – will become Leader of the Opposition on 12 September. Although he’s avoided setting out specific personal tax increases, the Member for Islington North has made it clear “the wealthy” (and large corporations) ought to pay more tax in order to tackle the deficit.

Now my fellow columnist Iain Macwhirter has been arguing that Mr Corbyn’s agenda is virtually identical to that espoused by the SNP at the recent general election, although that relies on a fairly selective reading of their respective manifestos. True, both advocate unilateral disarmament and opposition to austerity (although that latter aim has to be heavily qualified), but beyond that the similarities are superficial at best.

Indeed, until recently the current First Minister has been rather quiet on the subject of Jeremy Corbyn, while her predecessor has repeatedly distanced himself from his economic policies. “I don’t agree with Corbyn on a range of things,” wrote Mr Salmond in a recent newspaper column, while adding that he’d often been “right” on international affairs, a curious thing to say given Jez’s opposition to NATO and sympathy for Russian expansionism.

Asked about the rise of Corbyn at the stimulating Beyond Borders festival at Traquair House on Saturday afternoon, all Ms Sturgeon could muster was an anodyne comment about it betraying a “massive appetite for change”. Even more revealing was an articulate question from an audience member challenging the First Minister about her party’s focus on “wealth” and economic “growth”. Wasn’t there a case, he argued, for Scots to contribute more in order to tackle inequality?

Ms Sturgeon – another politician fond of deploying “radical” rhetoric – completely ducked the question. It was a debate, she replied blandly, she was sure would be had in the run up to next May’s Holyrood election. Under fire from another lady about fracking, the First Minister also demurred, emphasising the current moratorium but pointedly refusing to join in the left’s blanket opposition to the process. Her government, she added, would make a decision based upon the evidence (unlike, for example, GM crops).

These exchanges served to highlight a gap that has always existed between the SNP’s rhetoric and its record in government, something I’ve been banging on about for several years. The party has long been adept at latching onto certain issues in order to appear more “radical” and left-wing than they actually are, not least nuclear weapons. Recently, for example, the First Minister added her name to the CND’s “Rethink Trident” pledge, a politically cost-free move that conveniently keeps the party’s left-wing on board.

But inevitably, this leads to frustration on the purist left. Yesterday the Sunday Herald reported that a new political party called “RISE” (Respect, Independence, Socialism, Environmentalism) will launch in Glasgow this Saturday. Describing itself as “Scotland’s Left Alliance”, if the SNP (or indeed the Scottish Labour Party) were genuinely left-wing then this wouldn’t need to exist.

In this respect Jeremy Corbyn is a red herring, for his opposition to independence means there’s little prospect of the Scottish left – having repudiated Marx and learned to love nationalism – returning to a Labour Party led by a genuine socialist. That more than anything else highlights the disingenuous vacuity of claims (for example from the SNP MP Mhairi Black) that “I didn’t leave Labour, Labour left me”.

There is a wider point in all of this, that as the SNP approaches its eighth anniversary leading a devolved government it runs an increasing risk (if it hasn’t got there already) of becoming what it claims to hate, a relentlessly triangulating, endlessly fudging party desperate to cling on to support from left, right and centre but never properly articulating what it stands for. In other words, New Labour.

New Labour, people seem to forget, was once wildly popular too, and as the SNP becomes more and more a natural party of government while being outflanked on the left both nationally and domestically, it’ll become increasingly difficult to invoke radicals like Thomas Muir when they’re the ones arguing against genuinely radical reform.