Delivering a speech that will delight Conservative Euro-sceptics and dismay pro-Europeans like Kenneth Clarke and Michael Heseltine, the Tory party leader echoed the long-standing warnings of Lord Tebbit - that extremism, and violence could be whipped up by the creation of an artificial European superstate.
"Push political union beyond its limits," he said at the Fontainebleau business school he himself attended, "and you jeopardise the very peace, stability and prosperity which Europe's post-war statesmen were so anxious to secure. My fear is that the creation of a single currency will take European political union well beyond its acceptable limits."
For good measure, Mr Hague noted that the euro would be irreversible, and added: "One could find oneself trapped in the economic equivalent of a burning building with no exits."
But it was his warning against the political consequences of the drive to a superstate that will excite the Euro-sceptic right of his party.
"The lesson of Yugoslavia and the Russian Federation is that it is dangerous to force disparate peoples into a common political unit unless they already feel a sense of national affinity," Mr Hague said. "In Asia, those countries that have had the most violent reactions to the financial crisis have been those countries that do not have the safety valve of democratic elections. How will the peoples of Europe react to a recession without the electoral means of changing the people responsible?"
In a speech riddled with fear and foreboding, Mr Hague said: "I fear that the European Union is in danger; in danger of accepting without debate a political destination agreed 40 years ago; in danger of proceeding with political integration not because it is right, but because it is said to be inevitable ..."
Those fears were fuelled by economic, strategic and political arguments, but Mr Hague added: "I fear that a single currency could push us beyond the limits to union ...
"It would be to cross a line and abandon the independence of nation states with all the consequences for the future stability of Europe which I have set out today.
"The centre would have more power than the component parts. It would have neither legitimacy nor accountability since there can be no real accountability except in nation states.
"That is why I fear the political consequences of the single currency. For this reason the British Conservative Party is against British membership of the single currency now, and subject to a ballot of party members, intends to oppose it at the next general election."
Earlier, Mr Clarke, the former chancellor, warned that if Mr Hague could not reunite the Tories over Europe, "we aren't going to win any elections, we aren't going to come back from Opposition."
He urged his leader to go beyond the familiar litany of opposition to the euro for another nine years - through to the end of the next Parliament. "We have had 25 years since we signed the Treaty of Rome of people telling us that our national identity is at risk and our democracy is threatened. It hasn't happened."Reuse content