It is fair to say Philip Hollobone and Peter Bone don’t think much of David Cameron’s government. The clan leaders of the so-called Tory Taliban were responsible for the ‘alternative Queen’s Speech’ the other week which included moves to ban burqas, bash gypsies and wallop wind farms.

On the other side of the political aisle, activists from the People’s Assembly Against Austerity don’t think much of Labour either. One of their luminaries, PCS general secretary Mark Serwotka, spelled out why in his Staggers piece last week, berating Ed Miliband’s repositioning on welfare and spending as "economically stupid" and "politically inept".

Both can be dismissed as trumpet blasts from the political margins but they are indicative of something that our political leaders know only too well: British politics, as we have known it, is on the way out.

For 80 years, our system has accommodated large, conglomerated parties of the centre-right and centre-left, a small liberal party and assorted nationalists and unionists. This settlement has proved remarkably resilient in seeing off pretenders before, most notably the Social Democratic Party in the early 1980s, but the edges are now starting to atrophy, leading to fractiousness and fragmentation.

It starts at the edges but it really affects the centre, with powerful disintegrative forces pulling the two main parties towards the extremes, with centrists in both parties clinging on for dear life. As the Tories leach support to UKIP, Cameron moves rightwards to counter their advance.

Labour, meanwhile, faces a different challenge. It doesn’t have to counter an exogenous threat; recent events focusing on Unite’s modus operandi in parliamentary selection battles shows its problems are closer to home. The duty of trade unions to represent their members’ interests sees most reject austerity. This will become increasingly at variance with Labour’s more pragmatic approach as the party begins the process of staking a claim to the centre-ground and detailing its plans around deficit reduction and governing a radically downsized state.

As the party’s largest affiliate and biggest financial backer, with £8.4m donated to party coffers since 2010, Unite is currently pondering a merger with Serwotka’s more radical PCS (which isn’t affiliated to Labour) presenting the risk that a new super-union may disaffiliate from the party given the growing disagreements over economic policy, a move which would also scupper Labour financially.

Although it is the Tories who are publicly riven on issues stretching from gay marriage to HS2, Labour’s divisions run deeper. Social democracy, stripped of the ability to use the heft of the state to create a more equal society, suggests that Labour’s nervous breakdown is on its way, with the lack of hard detail about its direction currently serving to disguise tensions that go to the heart of what the party is for and in whose interests it governs.

Could either Labour or the Conservatives break apart? Traditionally the costs of establishing a political party and a hostile first-past-the-post electoral system, which makes it difficult for newcomers to gain electoral traction, has prevented this happening. But UKIP’s recent success is perhaps showing that it is possible to break the mould (although Farage still has to translate opinion poll results into actual seats).

Yet beyond the philosophical differences within our main parties lie deeper structural problems. Membership and participation levels have tumbled to all-time lows. Even allowing for a spike in new members following the 2010 defeat, Labour’s total is now half what it was in the mid-1990s. The Conservatives, with two million members in the 1950s, are now down to a tenth of that figure, with around 180,000 today. Meanwhile UKIP, with 30,000 recruits, is on course to overtake the Lib Dems, who have lost 35 per cent of their members since entering the coalition.

The emergence of a four-party system could see Labour win the next election with as little as a third of the popular vote, a prospect that should horrify party strategists, with "one nation" politics becoming a hollow boast if two-thirds of the electorate back other parties. But the rot goes far deeper than just the state of our parties. As few as six out of ten people now bother to vote in general elections – down from 78 per cent as recently as 1992, with the Electoral Commission warning that at least six million people are not registered to vote at all.

The crackpots of the Tory right and the purists of the anti-austerity left are easily dismissed as unrepresentative ultras, but their very existence – and their growing strength - serves to tell us that our stable, predictable system of party politics is now breaking apart.