George William Joy’s painting “The Death of General Gordon” depicts the defiant pose of a British officer about to be killed by religious zealots in Khartoum.

Looking at it, as I did at Tate Britain’s “Artist & Empire” exhibition on Sunday morning, it’s difficult to avoid the contemporary parallels, for Gordon was killed by followers of the self-proclaimed “Mahdi”, the messianic redeemer of the Islamic faith, during a religious revolt.

In the late 19th century the British response was relatively straightforward, and memorably brutal: at the Battle of Omdurman troops wielding Maxim guns routed the Mahdist army, killing around 10,000 enemy fighters.

Now the sun may have set on the British Empire long ago, but today’s international politics – albeit significantly more advanced in diplomatic, military and technological terms – don’t seem so far removed from the era of imperial adventurers like General Gordon.

Indeed the ghost of empire still haunt politics 130 years later. On the Left figures like Labour leader Jeremy Corybyn associate British military action with post-imperial grandstanding, while many on the Right all too readily embrace intervention as they seek to recapture an age in which a quarter of the globe was coloured pink.

And just as colonial policy led to Gordon’s death in 1885 (the Mahdi objected to Anglo-Egyptian administration of Sudan), previous interventions have contributed to (but not solely created) the fiendishly complex situation in the Middle East. Almost everyone is agreed that ISIS has to be tackled and defeated, but the more pressing question is by what means.

Today, in an undoubtedly rancorous atmosphere, the Labour Party will try to firm up its hitherto chaotic response, while by Wednesday or Thursday it looks likely the House of Commons will be asked to approve (or reject) an extension of airstrikes from Iraq to Syria. MPs have been consulted before – I well remember the drama of that evening in 2013 – but this time it seems the Prime Minister will persuade a majority.

Yet that doesn’t mean David Cameron has won the argument, indeed although Downing Street’s choreography over the past week or so – in terms of tone, consultation and positioning – has been impressive, the intellectual side of the balance sheet still seems to me insubstantial. Air strikes (as distinct from military action) appear to have become an end in themselves, an end that will justify the means.

As one SNP MP put it to me, “it feels like we’re doing something just for the sake of doing it”, and of course that isn’t a very compelling reason. But as the journalist Matthew Parris observed in a recent column, it will happen anyway, “Britain will join the bombing because it’s the kind of thing Britain does”.

Indeed a lucid report from the Foreign Affairs Committee, to which the Prime Minister responded last week, acknowledged the “powerful sense” that “something must be done” in Syria, but also concluded that the focus on air strikes was a “distraction” from the much bigger (and of course more difficult) task of resolving that country’s protracted civil war. The committee also sought “further explanation” on seven points, but it’s difficult not to conclude that – the question of legality aside – the UK Government still hasn’t provided them.

Furthermore the report is a product of that rare thing, genuinely evidence-based policy making, so while many witnesses acknowledged that a decision to extend air strikes into Syria would be welcomed by coalition allies, they also believed it would have little more than a “marginal” impact. Experts told the FAC that without “reliable” allies on the ground to assist with targeting and consolidation of recovered territory, the “multi-layered” nature of the conflict would mitigate against tangibly positive outcomes.

The Prime Minister has attempted to neutralise that concern by claiming 70,000 troops – which must be of moderate Sunni Arab origin – could be found among a disparate group of factions within Syria, but that seems far-fetched; Nicola Sturgeon called it an “heroic assumption”, which was a diplomatic way of saying complete nonsense. Who’s to say those troops – even if they exist – would be willing to operate together as a single anti-ISIS force, or that they’d have the capability to do so?

Formally, meanwhile, the SNP remain in “listening” mode, but it seems likely its 54 MPs (as well as two Independent Nationalists) will vote against. I think, on balance, they are correct to do so: the Paris attacks may have changed the mood in Parliament and the country, but they haven’t altered the weaknesses in the underlying rationale for extending airstrikes. As the SNP’s deputy leader Stewart Hosie remarked yesterday, the one thing Syria doesn’t lack is “people dropping bombs on it”, and it remains unlikely that “the UK flying a few more sorties in Raqqa is going to make any significant difference”.

Of course this leaves the SNP wide open to accusations of a “do-nothing” approach (indeed, that was my initial response to its opposition), but that’s a curiously black-and-white way of assessing a situation replete with shades of grey. And while the SNP’s emphasis on a “diplomatic” solution still strikes me as unrealistic, Mr Hosie’s suggestion of disrupting the flow of oil and arms through IS (tacitly facilitated by some countries that ought to know better) was a constructive alternative.

Tone is important in politics, and over the past few weeks Angus Robertson, the SNP’s long-standing defence spokesman and Westminster leader, has got that right, not only at Prime Minister’s Questions (where he’s consistently asked the right questions) but in response to Mr Cameron’s statement last week. He has neither questioned the Prime Minister’s morality nor resorted to histrionics, as others in his position might have done, while North-East Fife MP Stephen Gethins has worked hard on the detail (so often lacking when it comes to SNP foreign policy) via the Foreign Affairs Committee.

Mr Robertson emerges all the stronger given the travails of Labour, indeed the official Opposition’s weakness strengthens Mr Cameron’s hand in holding a Commons vote sooner rather than later. Sure, there’s an argument that Jeremy Corbyn has handled his party’s response to Paris and the debate over air strikes ineptly, but at the same time his central point – essentially the same as that of the SNP – is correct.

But then the Leader of the Opposition is a victim of a proxy war, a wider internal battle over his leadership and the soul of the Labour Party. Granting his MPs a free vote later this week might serve as damage limitation, but the events of the last few days have probably made his position untenable, even if that doesn’t manifest itself straight away (for one thing, there’s no obvious alternative).

But transient party political squabbles are nothing compared with the issues at stake in Syria, and provide all the more reason not to lose sight of first principles: what is the political end game and what is the military plan? For all the words and analysis produced over the last couple of weeks, style over substance (as in the domestic arena) simply doesn’t cut it.