But in the European election results declared on Sunday, the equivalent figure was under 44 per cent, down from 49 in 2004. Britain’s ‘two party system’ is ebbing away. Indeed, the share of the vote won by the Conservatives, Labour and the Liberal Democrats together has slumped from almost 96 per cent in the 1987 general election to 57 per cent in this year’s Euro poll.

Of course, Euro elections are fought using a proportional representation electoral system, while Parliament still uses first-past-the-post. PR invites electors to vote in a more plural way and, against the backdrop of the Parliamentary expenses debacle, has this year allowed voters to vent their anger with the major parties. The 44 per cent overall vote for Labour and the Tories is the lowest in any national election since 1945. But even in Westminster elections the two-and-a half major parties are under threat. In 2005, the ‘others’, who exclude the Lib Dems, exceeded 10 per cent. This share will undoubtedly rise at the next general election.

The weekend’s Euro results saw the Labour vote fragment into pieces that were inherited by Greens, UKIP, the BNP, English Democrats, the Christian Party, the Socialist Labour Party, No2EU and various others.

No fewer than 15 parties won 0.5 per cent of the vote or more. Cornish nationalists put on a good show. Voters used the PR voting system to express, simultaneously, aggravation with the government while providing a hint about what they might do if the country moved to PR for local elections in England and Wales and for Parliament.

Some of the Labour defectors will return to the fold for Westminster elections. But others will get used to casting votes in a less tribal way. Changed perceptions of ‘class’ and less ideologically-based political parties within Britain have weakened the grasp of the Labour and Conservative parties. People often find it hard to discern a difference between the positions adopted by party leaders, who then resort to ‘yah-boo’ exchanges to cover their similarities. Polling suggests the public do not much like this aggressive and adversarial politics.

Because their memberships are now so much smaller than in the past, the major parties will find it hard to re-build their base. Activism has long been in decline. As successive governments have weakened local government, there is less of a political culture beyond Westminster than there used to be. In a country as centralised as Britain, people may well start to support exotic parties in an attempt to get noticed inside the bunkers of Whitehall.

Sunday’s European elections provide a flavour of electoral consequences the fragmentation and individualism that has evolved in Britain in recent decades. Given the chance people will increasingly experiment with new political parties. PR, for good or for ill, encourages such experimentation. Gordon Brown, David Cameron and Nick Clegg will face a challenge to stop the continuing advance of minority parties and ‘others’. A genie is out of a bottle.

Prof Tony Travers is a professor within the Government Department at London School of Economics (Via Telegraph)