Yesterday, former MP David Chaytor was jailed for expenses fraud, and next week's byelection marks the end of another MP's career for grossly over-stepping the mark. Liberal Democrat Elwyn Watkins might have won Oldham East and Saddleworth in May but was robbed by Phil Woolas, who told lies about his opponent in leaflets stirring race enmity. We wait to see if a local sense of injustice carries Watkins through or if the torrent of fury at Lib Dem betrayal of election promises emerges as the stronger force.

There are blogs and emails swirling around that call for ways of pinning politicians down, subjecting them to recall, scrutiny and condign punishments of all kinds. All politicians lie, that's the view. And of course they do, just like the rest of us, only more so. To operate a party system, so that we know what policies we are voting for, MPs must pretend to support things they dispute, like things they hate, and believe things they don't while uttering empty pieties they know to be nonsense. Political messages are black or white in an often grey world. Abandoning a measure of autonomy goes with belonging to a party: MPs should only resign over major questions, as too few did over Iraq. Strict obedience has become ever more obligatory as a gaffe-hungry media hunt down any minor frontbench deviation from the party line. But in exchange for this necessary equivocation by MPs, there should be a reasonable expectation that voters get most of the manifesto they vote for.

One of the worst ideas in circulation is to make manifestos legally binding, nailing parties to pre-election promises. The danger is that politics will increasingly end up in the courts, with judges, not voters, in charge. Democracy needs politicians to be judged in the court of public opinion. But you can see why people are thrashing around angrily for some redress – and not just those who voted Lib Dem. Most outrage is heaped on Nick Clegg, with his unctuous promise of a new, clean politics. He may always have been a neoliberal, but he stayed in the closet. Instead, his party was the safe haven for anti-political voters, keeping their hands clean by never supporting a party in power. No wonder Lib Dem supporters flee in horror: the "real world" he now claims to inhabit was never for them. Any junior coalition partner was bound to be steamrollered by Conservatives bent on shrinking the state. Lib Dem policies were make-believe mood music, never seriously designed to be implemented.

Far more shocking is the spectacle of Cameron and Osborne's unabashed, barefaced and premeditated mendacity. Begin with the great broad questions about which they so reassured voters. Three days before the election, Cameron said on the BBC's Andrew Marr Show, "any cabinet minister … who comes to me and says 'Here are my plans' and they involve frontline reductions, they'll be sent straight back to their department to go away and think again". Yet £81bn in cuts now rain down on frontline services.

Would VAT rise? A month before the election, Cameron said: "Our plans involve cutting wasteful spending … our plans don't involve an increase in VAT."

As for the NHS, "We will stop top-down reorganisations of the NHS," said the coalition agreement, yet now what health secretary Andrew Lansley calls his "revolution" rolls in. The coalition promise that "we will guarantee that health spending increases in real terms" has gone the same way. Two months before the election, Cameron eulogised universal child benefit: "I wouldn't change child benefit, I wouldn't means test it, I don't think that's a good idea." On education maintenance allowances, Michael Gove said, just before the election: "Ed Balls keeps saying that we are committed to scrapping EMA. I have never said this. We won't." On tax credits, the promise was to cut them only for families on £50,000, but the budget book shows families with an income of just £30,000 lose all credits. Liam Fox promised "a bigger army for a safer Britain", but it now loses 7,000 soldiers.

Never mind what you think about all these promises – some are more honoured in the breach than in the observance – but such breaking faith with voters is breathtaking. The list is long – prison for anyone carrying a knife; no cuts to the navy; keeping the child trust fund for the poorest third of families; no hospital closures; 3,000 more midwives; a two-year council tax freeze – and more. Bluster about bank bonuses, wellbeing, going green and family-friendly government were all deceptive conceits too.

The coalition answer is Greece – a perfectly timed crisis in a radically different economy and society that gave a god-sent excuse for ditching election promises. Cameron was hammering away again last week about the economic peril that awaits Britain. But that fig leaf is slipping. Instead, the disaster will be caused by the cuts he promised never to make as growth slows, services and retail falter, house prices slide, unemployment rises and pay falls further behind inflation.

But all politicians lie, don't they? No, in 1997 Labour was so terrified of breaking pledges that it stuck painfully and needlessly for two years to Tory spending plans and kept to policies that the former chancellor Ken Clarke laughingly said he never had any intention of following. Labour MPs were driven through the lobby in tears to cut single parents' benefits. Jack Straw carried out Michael Howard's two strikes and you're out "prison works" act. Every Labour manifesto promised no income tax rises, and only in its very last month after the worst crisis since 1926 did Labour finally raise it for top earners. Here were promises that would certainly have been more honoured in the breach – but Labour, facing a mostly hostile press, never felt it had the leeway for the slipperiness afforded to Conservatives. There was indeed Labour dishonesty, from Brown's hubristic "no return to boom and bust" to the greatest deceit of them all – Blair's 45-minute frightener and the dodgy dossier taking us to war in Iraq. But there was care about election promises.

As Labour feels its way cautiously back from resounding rejection, rebuilding trust will be a slow process. If Labour wins Oldham, voters will be avenging coalition broken promises. Under pressure to fire off a policy a day, the lesson Ed Miliband seems to have absorbed is not to make those rash pledges in the first place. Cameron's thunderingly misleading manifesto will be his albatross in the coming year.