When broken governments cling to power, disunited and bleeding authority, the cry inevitably goes up: “Surely they cannot go on like this?” The correct response, more often than not, is: “Oh, yes, they can.”

The coalition has not yet hit the levels of debilitation reached by Labour under Gordon Brown or the Tories under John Major. Those administrations staggered on through injuries worse than the collapse of Nick Clegg’s plans for House of Lords reform and his threat to retaliate against Conservative plans to redraw the boundaries of parliamentary constituencies. Those blows wound the leaders of the two parties but in ways that force them into a mutually supportive limp, so they can better hobble towards the electoral finishing line together.

There was evidence of that gruesome bond in Clegg’s statement on 6 August, when he confirmed that hopes of creating an elected upper chamber were dead. The Lib Dem leadership feels that Cameron has failed to honour a personal pledge to whip his MPs behind Lords reform. Yet that was the one portion of blame that Clegg pointedly refused to dish out in his televised eulogy for constitutional renewal. He accused Labour of playing “student politics” – backing Lords reform in principle; refusing to deliver it in parliament. He denounced Tory MPs’ betrayal of the spirit and letter of the coalition agreement. But public fulminations against the flakiness of the Prime Minister remain taboo.

Pretty fly

The episode is a classic case, says a senior Lib Dem, of Cameron “doing everything on the fly”. It is a criticism often voiced by Conservatives, albeit with different issues in mind. The Prime Minister, they say, fails to prepare the ground, neglects his homework, trusts too much in his persuasive charm and an ability to perform at the last minute under exam conditions. It is the way he treats everything from health reform to European summits.

Clegg could not name Cameron as the architect of his despair because, whatever their differences, the two men must maintain the pretence that their relationship is the dynamic engine of government. For the Lib Dem leader to admit he has reached the limit of what he can get the Prime Minister to do for him would be to accept the charge that his party is a helpless passenger on board a Tory train with unruly backbenchers as the locomotive.

Cameron did not push Lords reform too hard because he calculated that the risk of antagonising his MPs, reinforcing their suspicion that he dances too eagerly to Lib Dem tunes, was greater than the risk of short-changing his coalition partner. If Clegg doesn’t like it, Downing Street aides mutter, let him try his luck outside coalition and see how long he lasts. They know he won’t.

Cameron’s frustration is that he isn’t getting any credit from his own side for thwarting Lib Dem ambitions. That is partly because he has paid a heavy price in the potential loss of the boundary changes. The new electoral map, reducing the number of MPs by 50, would redress an old, anti-Tory bias in the system worth around 20 seats. Without the upgrade, Conservative prospects of winning a majority at the next election recede dramatically. Cameron has said he still wants parliament to vote on the matter, forcing Lib Dem ministers into the awkward (some Tories say untenable) position of opposing the government in which they serve. But the working assumption among MPs now is that the next election will be fought on the old boundaries.

Plenty of Conservative backbenchers are quietly happy about that. It spares them the pain of competing for selection as candidates in new constituencies. Besides, Cameron’s reliance on electoral cartography to do in 2015 what he couldn’t do in 2010 is seen by many as a symptom of failing strategic imagination. “We really should be able to win a majority with argument and ideas,” says one prominent – and so far un-rebellious – Tory MP.

That doesn’t cool Conservative rage against Clegg for the threat of sabotage, nor does it diminish disdain for Cameron for having befriended the saboteur. What really riles Tories is the way Clegg justifies his actions on the legalistic grounds that the coalition agreement – “the sacred text”, as senior Lib Dems call it – has been breached. The technicalities of what that document prescribes are disputed but such hermeneutics are beside the point. Tories resent being told they should have embraced Lords reform because they know that for Lib Dem MPs some of the charm of an elected senate lay in its repugnance to Conservative backbenchers.

The sight of Cameron’s blue army marching queasily behind an orange banner was to be compensation for the junior party’s dignity-shredding endorsement of NHS reform, welfare cuts and university tuition fees. Tories also note that the Lib Dems foresaw electoral ruin in the boundary changes and, despite having voted for them in parliament once already, were itching to renege. What Clegg presents as contractual propriety, Tories see as opportunism and vindictiveness.

Zero-sum game

The Lib Dems would be less mercenary if they were getting any credit for the parts of their manifesto that have been enacted – raising the income tax threshold; the “pupil premium” to target school funding at children from low-income backgrounds. But Tories like those policies, which in the zero-sum game of Westminster politics diminishes their value as trophies for the other side of the coalition.

Clegg had always envisaged a less tribal, more consensual, Continental model that cherishes cross-party compromise. Defeating that ambition, satirised by Tories as an attempt by the Europhile Lib Dems to import Belgian-style democracy to the UK, was an undeclared war aim of the rebels in the battle for Lords reform. They have won. That is a problem for the Prime Minister, too, since he remains dependent on Lib Dem MPs to govern.

Britain, it seems, has innovated its own peculiar model of coalition and it is not a very healthy one. The bonds holding the Lib Dems and Tories together are tight enough but they are looped around the necks of Clegg and Cameron so the forces pulling the two parties apart are checked in a way that strangles the political life out of their leaders.