With all due respect Stuart, I think you have the wrong end of the stick on a number of points. The current "lions led by donkeys & futile & needless slaughter" meme was a pacifist thing that began in a very small scale in the late 1920s when some of the war poets were picked up by the Bloomsbury Group et al; the same intellectual "elite" were also behind the similarly narrowly supported Oxford Peace Pledge Union business in the 1930s. They and the supposedly universal perspective they represent was never more than a very small intellectual clique which gained very little traction at that time because there were lots and lots of people about who had served in the Great War and who held a very different (and majority) view. The very common historical problem you have is that the latter didn't bother to set their view down as it was so blindingly obvious they didn't think there was any need, which has left a gap in the historical record ripe for folk with axes to grind to exploit for their own purposes. Despite the current "popular" perception the evidence shows that the majority view up until c.1939 was that the First World War had been a heavy but necessary sacrifice in order to stop Prussian/German militarism and put it back in its box. For proof take a look at how many First World War veterans turned out for Haig's funeral in 1928, a decade after it was all over, both the official ceremony in London and arguably more importantly the 30,000 at his actual funeral out in the middle of nowhere at Alnwick. They'd have hardly done that if they thought they'd been gulled into a needless and futile slaughter. Regarding the literary perspective, I'd suggest you look at one of the very few Other Rank memoirs based on a diary kept against regs at the time, Private 12768 by John Jackson; he was a Kitchener volunteer who served right through the War and he gives a diametrically opposite view to that of the War Poets including a retrospective conclusion he wrote ten years after to see if he felt the same then (he did). Another contemporary account, albeit in novel form but in the same vein is Frederic Manning's Her Privates We, and consider the mass market popular fiction published in Britain between the wars. There was shedloads of stuff about the Great War aimed at young males ranging from comics like Chums, Boy's Own and Champion to full on novels like those by Frederick Sadlier Brereton and W.E. Johns of RFC scout pilot and Biggles fame. Just about all of it flew in the face of the War Poet & pacifist stance and much of it remained in print right through the 1920s and 30s. Then as now only stuff that sells gets published, and I cannot see why the public would consistently purchase stuff for getting on for two decades & through the depression if they didn't agree with what it was saying.
The lefty bit arguably came in with the second wave of revisionism which appeared in the late 1950s/early 1960s with Clark's The Donkeys which IIRC Clark admitted years later was deliberately provocative tosh, and more importantly Joan Littlewood's 1963 pacifist stage play Oh! What A Lovely War which was turned into a film at the end of the 1960s. The latter tells you all about what 1960s left-wing pacifists and their assorted political fellow travellers thought of the conflict but very little about what actually happened between 1914-18 or more importantly what the people involved actually at the timethought about it. Despite this the Littlewood narrative has set the tone for the popular perceptions of that conflict (and indeed every other - consider the blond squaddy in Zulu asking "Why?") ever since. Blackadder Goes Forth is merely a 1980s update, the same narrative can be clearly identified at least up to a point in the ground-breaking 1964 BBC documentary series The Great War (there were shedloads of veterans about then - watch it & compare the number of interviews with the extracts from the war poets) and it has shaped the way the First World War is taught in schools ever since. I've seen it for myself in the c.40 secondary schools I've worked in over the last decade - the futile & needless slaughter line is peddled across the board in history teaching and is presented unquestioningly as context when looking at the War Poets in English Literature (not history note), not least because the vast majority of the teachers simply don't really know much about the topic. Indeed, having been exposed to the same stuff at schools themselves many simply don't realise that there is any differing perspective, and the recent focus on exam results and league tables has exacerbated the problem and encouraged such lazy teaching. The end result is half a century of deliberate misrepresentation being presented as verifiable historical fact, and not just in schools. The same view held sway until around the mid-1970s in universities and still does despite the work of folk like John Terraine, Peter Liddle, Richard Holmes, Hew Strachan & Gary Sheffield et al; have a look at Richard Evans view in the second link below - I've had to link articles from the Daily Heil as that is where Gove originally put out his piece with a response from Evans & Sheffield the following day. Personally I think it amusing that the folk who are trying to correct the 1960s revisionists are now accused of revisionism themselves. I think the old saw by Lenin or Stalin (IIRC) about repeating a lie often enough has rarely been so apt... 
BillB
Linkies:
Goves original article in the Wail (scroll down past the title piece) :http://www.dailymail...-academics.html
The response from Evans & Sheffield: http://www.dailymail...ools-argue.html
And an entirely predictable contribution from that ardent communist Knight of the Realm Comrade Tony Robinson: http://www.theguardi...first-world-war
Thought this might be of interest too from 2006: http://news.bbc.co.u...ine/5130386.stm
