If you had been looking at the British media in recent days, you would seen a lot about an MP called Heidi Allen. Until February, Allen was the Conservative MP for the consitituency of South Cambridgeshire in eastern England. She still represents that constituency, but the reason she featured in the news was that she has just switched parties.
Having left the Conservatives in February to help found a new party, Change UK, she has now joined the Liberal Democrats - the long-standing centrist party whose defining policy is opposition to Brexit. While both the UK's two main parties – the Conservatives and Labour - are divided on Europe, the Liberal Democrats support the UK's membership of the European Union. Allen says that she will fight the next election under the LibDem flag.
Among what might be called mature democracies, it is possible to distinguish two groups: those untries with very stable party systems, and those whose parties seem almost perpetually in flux. The United States might exemplify the first kind, with two major parties whose dominance is rarely challenged. 1992 was a rare election when votes for an independent, Ross Perot, may have helped deprive George Bush senior of a second term. Germany's party system is also quite stable, with a conventional spread of parties from left to right and the CDU and the SPD occupying the right and left centre ground. Support for smaller parties ebbs and flows; but the essential pattern remains set.
On the other side might be France, where parties seem to be in something like constant flux. The main centre-right grouping - broadly speaking, the Gaullists - has reshaped and renamed itself many times. This fluidity is partly what enabled Emmanuel Macron to resign from the Socialist government of Francois Hollande, and sweep to power at the head of his own centrist movement, En Marche - now a party called "la Republique en marche".
Whether on left or right, personality in a party leader counts for much. Even that seeming fixture of French politics, the far-right National Front, dominated by the Le Pen family, recently renamed itself the National Rally party. France shows that party fluidity is not unique to countries where a multi-party system is something new.
What seems unusual, though, is for a country to switch from one category to the other. Yet this is what seems to be happening in the UK today. It has had a more or less stable two-party system for the best part of 300 years. To take just the last century or so, UK voters had mostly had to choose between the Conservatives on the right and Labour on the Left, with the Liberals – more recently the Liberal Democrats - a much smaller party in the middle. The biggest ruction in recent years was in 1981, when several senior Labour politicians broke away to found the Social Democratic Party. Within less than a decade, however, it had joined forces with the Liberal Party to become the Liberal Democrats, and the two-party system was back.
What is happening now is rather different. It could even become the splintering of the whole UK party system, the actual "breaking of the mould" the SDP had hoped for. And it is all because of the stress that has been placed on the system by the Leave victory in the 2016 EU referendum.
Labour and the Conservatives have long been divided about EU membership. So long as Europe was just one political issue among many, however, they could remain united as parties because their members agreed on almost everything else. The two-party structure remained in place also because the chief euro-sceptic party, the UK Independent Party under Nigel Farage, was unable to break in to mainstream parliamentary politics. Even though it won the largest number of UK seats in the 2014 EU parliamentary elections, it could never win even one seat in the UK Parliament because of the first-past-the-post electoral system.
EU parliamentary elections use a system of proportional representation. The Greens and every small or new party faces the same problem, which could be seen as a defect of UK democracy. EU parliamentary elections, in contrast, use a system of proportional representation.
Ukip's effective exclusion from the UK Parliament may be one reason why the Leave victory was so rarely predicted before the 2016 referendum. Now, though - and perhaps in part because the process of actually leaving the EU is dragging on so long – Brexit is THE subject that defines UK politics. The problem is that the party system does not reflect that. The only overtly pro-Brexit party, Ukip, has no members of parliament, and the only overtly pro-EU party, the Liberal Democrats, returned only 12 MPs at the 2017 election. The two big parties remain divided.
Could it be, though, that the UK's long-frozen party political system is starting to crack? The first moves came in February when Heidi Allen and several other pro-EU MPs resigned from the party to form a new party, which became "Change UK". It failed to gain the following its leaders had hoped, but the process of fragmentation did not stop. Since the early summer, four pro-EU Conservatives and three pro-EU Labour MPs have sought a new home with the Liberal Democrats.
The fracturing was accelerated after Boris Johnson became Prime Minister in July. One of his first acts was to require all members of his Cabinet to sign up to "deliver Brexit". He had no intention of balancing different EU views in the Cabinet, as Theresa May had tried to do. He then suspended no fewer than 21 Conservative MPs from the parliamentary party - they included several former ministers and several party luminaries - after they had opposed the Government in a crucial vote. There is talk that some of them could create a new centre-right party or join the LibDems, too.
At the other end of the Conservative spectrum are those who might be tempted to defect to Ukip, if they lose faith in Boris Johnson's ability to take the UK out of the EU. This sort of disillusionment could give Ukip a number of MPs at the next election. With pro-EU voters moving towards the LibDems and pro-Brexit hardliners veering towards Ukip, the dominance of the two big parties could be challenged, if not eroded, at the next UK election.
Whether the process will go further, to the point where the UK perhaps develops a wider spread of smaller parties on German lines, is likely to depend on two factors: how strong traditional loyalties to Labour and the Conservatives remain, and whether - as a longer-term consequence of the current parliamentary stalemate - the UK might one day switch to a proportional electoral system. But this is not on the horizon yet.
What is certain, though, is that UK voting patterns are at their most volatile ever in modern times. This was borne out by research published this week by the British Election Study - which brings together work by Oxford and Manchester Universities. It found that across the three last elections (2010, 2015 and 2017), almost half of those who voted did not vote for the same party each time. In other words, loyalty - which was often related to class, especially in England - has been breaking down and the results of any new election are highly unpredictable. It traced this change to the effects of several "shock" events: the financial crash of 2008, the arrival of so many new EU migrants, and - something that has, in its view, not yet fully played out - Brexit.
Theresa May called an election in 2017, expecting that the Conservatives would increase their majority. The opposite happened. Boris Johnson may choose or be forced to call an election before the year's end. It looks as though any campaign will be the most fragmented of any within memory; and only a fool would predict the result.