Power to the people: The leaders of Britain's political parties underestimate us at their peril

From time to time the English defy their rulers. The surge of support for the Liberal Democrats in this election is the latest example. By their nature, these outbursts are at once powerful yet inchoate, massive yet leaderless. Anything can become tinder to the raging fire. The Prime Minister's private remark, overheard yesterday, to the effect that a voter to whom he had just been speaking was "a bigoted woman" is just such an example.

Nick Clegg is not the creator of this insurrection; he is the beneficiary. Tonight, in the last of the TV debates, Mr Clegg must demonstrate that he is not merely being pushed from behind by a mighty demonstration of people power, flailing helplessly about as it propels him along. He must be able to transform public anger into coherent policy. If he succeeds, this insurrection will become more powerful than those that have preceded it.

I say the English periodically defy their rulers because the dynamics of protest are different in Scotland, Wales and Northern Ireland. The last occasion of this kind took place in February 2003, when 1 million people marched in London to protest against the decision to invade Iraq. It was the largest demonstration that this country has ever seen. Somebody must have organised it, but at the time I had no idea who it was and I don't know now. It was as near to spontaneous as makes no difference. It did not stop the war. But those who disregarded the warning have paid a heavy price in reputation and honour.

An earlier example was the death of Princess Diana. Her funeral drew 3 million onlookers and mourners to London. This display of admiration and sympathy for the Princess also implied criticism of the way members of the Royal Family had treated her. The Queen responded by addressing the nation on television. Then, when Earl Spencer in his funeral address in Westminster Abbey appeared to share the feelings of ordinary people, a ripple of applause went through the crowd outside and was broadcast to the entire world. It was a rebuke than can never be forgotten.

Seven years earlier, Margaret Thatcher had faced the poll tax riots. These were a series of mass disturbances in British cities. By far the largest occurred in central London on Saturday 31 March, 1990, shortly before the poll tax was due to come into force in England and Wales. In the days before the demonstration, two "feeder" marches had followed the routes of the two mob armies of the Peasants' Revolt of 1381. There were violent clashes with the police. By midnight on Saturday, 113 people had been injured and 339 arrested. Partly as a consequence, Mrs Thatcher was forced to resign as prime minister in November of the same year and the poll tax was subsequently abolished.

These protests have three stages. They take shape, they make their point and then they subside. But they always succeed in changing things. In this election upset of 2010, the parliamentary expenses scandal is the biggest influence. This is what has caused voters to desert the two main parties. For it suddenly ripped the veil from our eyes. We could at last see clearly how low is the quality of Members of Parliament. We had been over impressed by stately titles for too long – Honourable Members, Privy Councillors, Knights of the Realm, Ministers of State, Secretaries of State and the like. As a result we had not comprehended the sordid reality of contemporary politics.

Surely these people, we had said to ourselves, cannot be on the make, cannot be too lazy to attend debates except when their votes are required, cannot have passed Bills without proper examination, cannot have acquiesced in a diminution of their powers in relation to the government of the day, cannot have been silent about the war in Afghanistan, cannot have carried these same careless habits into high office as ministers? But they have done so, unfailingly, repetitively. Three MPs are currently standing trial. Do we know of any other organisation of similar size to the House of Commons (650 people) that has as many as three of its number facing criminal charges? In fact a stricter reading of the laws of theft, embezzlement and fraud would have brought 10 times that number of MPs before the courts.

Yes, it may be said, but we need worry no longer because expenses cheating has been stopped. But that is to be twice blind. Regard the financial services sector as a warning. When one loophole in banking regulations or in the tax laws is closed, another is found. Bankers and politicians are similar in some ways. The bankers didn't "get it" when their bonuses were challenged; MPs didn't "get it" when their expenses rackets were exposed. Both habitually trade near the edge of respectable behaviour. Have the factual errors made by the three political leaders in the TV election debates been just understandable lapses of recall with so much to remember or, as I believe, a characteristically slap-dash attitude to the truth?

A less striking influence on voters but equally insidious has been repeated failures in the delivery of public services. The horror stories may or may not be representative, but they have struck home. The 800-page report on the Mid Staffordshire NHS Foundation Trust, which, through mismanagement and poor practice, caused some hundreds of avoidable deaths between 2005 and 2008, read like a report from the Crimean war before Florence Nightingale arrived. A woman described visiting her elderly mother: "She was completely naked and if I said covered in faeces, she was. It was everywhere. It was in her hair, her eyes, her nails, her hands and on all the cot side, so she had obviously been trying to lift her herself up or move about, because the bed was covered and it was literally everywhere and it was dried. It would have been there a long time, it wasn't new."

Go from these Abu Ghraib-like scenes to a small incident reported earlier this week. A man went into a police station to report that vandals had damaged his car. However, rather than finding an officer who would write down the details and decide what action was required, he was told that crimes could not be registered in person; he must telephone to do that. So part of the protest movement has in its sights a state that is distant yet unduly inquisitive, uncaring yet expensive, bureaucratic yet ineffective.

People have also realised there is not as much difference between the rival policies as is made to appear. "They are all the same" is a common remark. And history supports this view. The Conservative Party of the late 1950s and early 1960s accepted the Welfare State created by the post-war Labour Government led by Clement Attlee. In turn Mr Blair left intact large parts of Mrs Thatcher's work. Moreover, people understand that in government policies are shaped more by events than by philosophy. As for the huge budget deficit, for instance, the differences between the parties are all of timing, not of principle.

In the case of the dramatic upsurge in Lib Dem support, we are still at the beginning. At least we are so long as Mr Clegg doesn't fail badly on TV this evening. We can all participate if we wish to do so. In the same way that we could have chosen to have gone on the Iraq march, or travelled into central London for Princess Diana's funeral, or made a disturbance about the poll tax, so on 6 May, election day, we can join the protest if we wish.

It no longer feels unsafe or eccentric to do so. A YouGov poll, suppressed last week by the Murdoch newspaper that commissioned it, showed that voters fear a Liberal Democrat government less than a Conservative or Labour one. YouGov also found that if people thought Mr Clegg's party had a significant chance of winning the election, it would gain 49 per cent of the votes, with the Tories taking 25 per cent and Labour just 19 per cent. We are, then, on the very edge of a peaceful revolution in British politics.

It can fairly be said that the trouble with voting Lib Dem come what may is that the more closely the behaviour of their MPs in the last Parliament is examined, the more the party appears to be part of the problem. Its High Command, for instance, sent instructions to Lib Dem MPs on how to exploit grey areas in the rules for parliamentary expenses. They were also told to be "'imaginative" because "there is lots of scope". In practice they are just as sleazy as the other two parties.

Rightly or wrongly, however, people don't care. Another recent poll suggested that 25 per cent of potential Lib Dem voters admitted they knew little or nothing about the party's plans for Britain. But they do know something else: the present political establishment is unworthy of their support.