Every politics student knows Vernon Bogdanor's argument that Britain does not have a codified constitution because it has not had a constitutional moment. The French and American constitutions emerged from revolutions. Germany and Italy owe theirs to the Second World War. In Britain we consider ourselves above such things. Like Charles Dickens's Mr Podsnap, we imagine that our unwritten constitution was "bestowed upon us by providence", and that "no other country is so favoured."
As Gordon Brown sought advice from the Cabinet Secretary yesterday, he should have recognised how foolish such complacency now is. Voters will soon tire of politicians preaching that post-election horse-trading between parties is common in Europe. Such affection for continental practice is not only novel, it is deluded. When European leaders negotiate they do so according to rules. Our lot are making it up and it is time they stopped.
Election 2010 has delivered Britain's constitutional moment. If we do not now codify the rules upon which our democratic system operates, the security and prosperity we treasure will be damaged and the United Kingdom may collapse. Why? Because in the years since 1997 Labour introduced a piecemeal constitutional revolution that now threatens unintended consequences. The most blatant anomalies arise from the devolution of power to the Celtic fringe.
On Thursday, voters in Scotland elected 41 Labour MPs, 11 Liberal Democrats, six Scottish Nationalists and one Conservative. English voters elected 297 Conservatives, 191 Labour and 43 Liberal Democrats. The populations of England and Scotland are 51.4 million and 5.2 million respectively. But Labour's haphazard constitutional geometry allows the possibility that the smaller part of the UK may determine the future of the larger one.
If David Cameron and Nick Clegg fail to agree terms by which a Conservative-led government can take office, the Liberal Democrats will enter discussions with Labour.
No anomaly there, it happens throughout the democratic world. What does not happen is the formation of a coalition government in which MPs guaranteeing the passage of controversial legislation can support it in the certainty that it will have no consequences for their own constituents.
If a Labour/Liberal coalition emerges, an English Conservative voter who backed the party out of sympathy for its education policy may find that policy blocked by the votes of Scottish Labour MPs. If a Scottish voter faced the same risk of being stymied by a Conservative-dominated coalition this would be fair. But Scottish voters are insulated from policies they oppose. Their schools are governed from Holyrood where an Executive elected by Scottish votes alone holds office.
My home county of Kent, which has just elected 17 Conservative MPs from its 17 parliamentary constituencies, will, along with the rest of England, be governed by the UK parliament. Scotland, Wales and Northern Ireland will have their domestic affairs, including education, health and the provision of social services, administered at home.
This was the point of devolution. Scotland did not vote for the poll tax but got it first. Wales loved its coal mines and Maggie closed them. So the Scots and the Welsh sought home rule to protect them from a party they despise. Good, but the English have chosen David Cameron's Conservatives and, in the absence of formal rules, they may be denied him.
This may look fine and dandy to Britons now immersed in the political culture of devolution. They have rules and proportional representation in devolved elections. To undevolved, unmodernised England it is a stark affront. It has come about because Labour could revolutionise the British constitution without consent and without codifying rules for the new game it invented.
Conservatives must share the blame. Their traditionalists spurn written constitutions as immigrant contraptions concocted to demystify the comfortable rituals of British democracy. But now Mr Cameron's modernisers must prove their modernity. Labour has murdered the rituals. In their place stands an incoherent morass of laws that may soon persuade English voters that the way to get a government they want is to end the union.
A Conservative Party committed to the British national interest would have to be furious to abandon Scotland, but it would not have to be mad. Many in its ranks favour a divorce that would guarantee them rule by their own representatives. Their argument will only grow stronger if Scots, Welsh and Ulster MPs choose the government of England. Better by far to agree rules that turn rhetoric about equal rights into incontrovertible guarantees.
In the name of the people, the American constitution promotes liberty, justice and welfare and "a more perfect Union." At this defining moment for British democracy it is plain that we need a rulebook at least as clear and ambitious.
Labour was able to play fast and loose with the constitution because opposition politicians thought the bipolar seesaw of post-1945 politics was permanent, and parliamentary sovereignty would eventually give them the chance to reverse all changes. Those assumptions were utterly wrong.
Parliamentary sovereignty, according to which Westminster can make or unmake any law, is already dead, and not just because European Law takes precedence. Devolution too is irreversible and it has profound consequences for English voters who were not invited to approve it.
One indecisive election has exposed that flaw and several more. Why should convention decide how long a defeated prime minister can cling to office? Is it reasonable that a new system of voting can be introduced without popular consent?
Election 2010 has inched Britain closer to modern politics. We need modern rules to keep the process clean and transparent. A constitution can deliver justice and preserve the Union that makes Britain greater than the sum of its parts. Put that into the coalition talks, Mr Cameron, and make it stick.
Tim Luckhurst is professor of journalism at the University of Kent and a former editor of 'The Scotsman'