"You started it. You invaded Belgium" is what Basil might have shouted at his guests if he had been desperately trying not to mention not that war, but the one which came first. Yet that joke would have been lost on most people. For Poland is still the most popular choice when people are asked to identify the cause of Britain's 1914 declaration of war on Germany, which came almost exactly 99 years ago. Just 13 per cent recall enough of the story of "plucky little Belgium" to get the answer right.

"You started it. You invaded Poland" shouted Basil Fawlty, as the hapless Torquay hotelier's attempt to not mention the war to his German guests unravelled into goose-stepping embarassment. The Fawlty Towers' satire on the British cultural obsession with Hitler and the Nazis still strikes a chord, 30 years on. The cultural power of the Second World War could even threaten to overshadow next year's First World War centenary.

The centenary challenge is that most people struggle to keep the two wars apart. "Britain at war" conjures up much resonant imagery for many people, but the Second World War which dominates. Beyond images of mud, trenches and barbed wire - and troops playing football during a Christmas truce - the fog of war descends. Researching public understanding of the centenary for British Future's new publication Do Mention the War , we often found the first world war getting lost in the second. "Rationing" featured as one of the most immediate top of mind associations about the First World War when we held public workshops around Britain.

"I've put rationing - but was that one or was that two?" was a common refrain. Four-fifths of us do know that this was a war with Germany, which is a start, but that does leave a surprising proportion who don't. (Three per cent think Britain and Germany were allies in the Great War trenches; while four think we fought against France). Clear majorities can identify France (71 per cent) and America (70 per cent) as British Great War allies too, but not Russia (34 per cent). People are three times as likely to place Japan on the other side as to know that they were an ally in the first of the two world wars.

Almost everything else is now minority knowledge. Most men (58 per cent) can name-check Archduke Franz Ferdinand, as the victim of the assassination which begins the war. Only four out of ten women can do so, reflecting a significant gender gap over knowledge of the war. Very few people could explain how the assassination led to Britain declaring war. "I think it began when an Archduke shot an Ostrich because he was Hungry", said Private Baldrick in Blackadder Goes Forth, one of the main sources of both knowledge and mythology of the Great War today. Serbia is certainly a forgotten ally, and even Austria-Hungary an unfamiliar 1914 enemy to most people.

Yet shaky public knowledge is combined with a strong sense that the centenary matters. Why should we care so much about a war of which we now know so little? It is the scale of the loss of life commands respect - especially when people hear about the scale of a conflict in which there were nine million military deaths, a million of them British. People also articulate a strong sense that both world wars provide indispensable foundations of our national identity.

Why that matters is often articulated personally too. The First World War has moved from memory to identity, with nobody who experienced the trenches directly still now alive. Yet people do think it matters that their children now enough about the lives of their great-grandparents to be able to pass that on, in time, to their children. Knowing how our past, present and future are connected is an important part of how we understand what it means to be a family. It is an important part of what it means to be a national community too. If we do believe it is important to have a shared history, we may now need to first learn what we want to remember.

The research does make the case for school history offering a clear narrative of the defining events of British history. Younger Britons were sometimes more likely to be spectacularly wrong: 7 per cent of the under 24s think Margaret Thatcher was the Prime Minister when the war ended in 1918. But age did not always trump youth on knowledge. Young people did choose Belgium ahead of Poland, with older Britons being more likely to confuse the two wars. They were as likely to know about Archduke Franz Ferdinand (and only 3 per cent of the under-24s thought it was Kaiser Chiefs who had been shot). There was no age gap on knowledge of Commonwealth troops, though only just over four in ten know about this - though most do not know that Australian, Canadian or Indian troops took part - suggesting it may be at least one element which has become more prominent in schools over the last decade or so.

Sayeeda Warsi wrote yesterday of her determination to increase that awareness of Commonwealth troops as we use the centenary to learn more about the history of this country. The public think that matters. By 80 per cent to 4 per cent people agree that 'it is important for integration today that all of our children about taught about the shared history of multi-ethnic Britain', a meaning of the centenary with similar mainstream appeal to remembering the debt to those who died for Britain, using the centenary as a chance to learn, and the importance of peace and reconciliation as a theme of the centenary.

But there is a positive finding too, about how much appetite there was to seize the centenary as a "chance to learn" more of our forgotten history. Women particularly talked about museum trips, TV programmes and even the children's homework as a chance to find out what they wished they had remembered from school. (Men may have agreed, but were often markedly reluctant to acknowledge the gaps in their own knowledge). An increasing number of historians now question the traditional understanding of World War One and World War Two, with some shifting towards seeing the three decades from 1914-45 as a long European crisis.The great British public, in their own deep conflation of the two conflicts, may have arrived somewhere similar to the scholarly avant-garde, but perhaps not from any detailed scrutiny of the historic evidence.

The four years of the centenary from 2014-18 will not only be marked by moments of solemn commemorations. They should also offer many chances to reopen public debates about some of the biggest questions in our modern history. Was Britain right to fight, or should it have steered clear of continental entanglements? Was it vital to block the Kaiser, or did the conflict make the rise of Hitler possible? Should the focus of the centenary be on the pity of war, and the futility of the lives lost, or do we believe that those who died did so to protect our freedoms? Could the multi-ethnic armies who fought for a British Empire teach us anything about integration in a democratic age? How should former enemies remember together, and what lessons about war and peace are relevant in our different world today?

Those all should be important, contested, arguments about how the Great War shaped the century which followed. Brushing up on at least a little bit of history could help us to have those arguments about how we became the countries that we are today. With a year to go to the centenary, we do need to mention the war. But not that one, Basil - the other one.