This has been a year in which, politically, everything has changed. At the end of 2009 Gordon Brown was in Downing Street, propped up by Peter Mandelson. The Prime Minister's authority was about to be challenged in a coup attempt by two former ministers. An end-of-era feel haunted the Government. Twelve months on, David Cameron resides in Downing Street, supported by Nick Clegg. Despite some backbench grumbling, there is little expectation of a direct challenge to the Government's authority. A new political era has begun.

Several leaders were given a sharp lesson in the vicissitudes of politics in 2010. Mr Cameron was widely expected to lead his party back to power after 13 years in the wilderness of opposition at May's general election. But instead, the Conservative leader ended up forming Britain's first coalition government in 65 years.

Mr Clegg shot from relative anonymity to public adoration for his performance in the election campaign's televised leaders' debates (with one poll suggesting that the Liberal Democrat leader was almost as popular as Winston Churchill). But what went up has come down. Now the Liberal Democrat leader finds himself a hate-figure among students for reneging on his party's pledge to scrap tuition fees. His is not the only star to have fallen. David Miliband began the year contemplating the Labour leadership and ends it contemplating the end of his political career, after being beaten to the job by his younger brother.

But the significance of this year extends far beyond the political soap opera. At the end of 2009, many Britons had been sheltered from some of the worst effects of the recession as interest rates fell and the Government continued to spend in order to support the economy. But George Osborne's emergency Budget in June set in motion the most ambitious fiscal consolidation since the 1970s, as the Coalition decided that a potential threat to Britain's creditworthiness was a greater danger than high unemployment.

The pressure of financial retrenchment has not been universally malign in its consequences. The Justice Secretary, Ken Clarke, is using the opportunity to reshape the penal system for the better. Some of the previous Government's expensive and illiberal paraphernalia, such as ID cards, have been ditched. The Government has also postponed a looming decision on whether to renew Trident until the next parliament. But for every victory for progressive causes, there has been a setback. Legal aid is being squeezed and financial support for disadvantaged secondary school students eroded. And this is only the beginning.

Talk of an ethical revolution in public life, the so-called "new politics", has been overblown. The behind-the-scenes skulduggery and media management remain. Last week's sting by The Daily Telegraph has embarrassed some Liberal Democrat ministers. And the third party itself has haemorrhaged support as a result of the pact with the Conservatives. Yet the country as a whole has shown that it is comfortable with a coalition government. And the Coalition itself has not buckled under the strains of office. Predictions that May's hung parliament would soon be followed by a new election have been confounded.

Whatever view one takes of the Coalition's policies (and this newspaper has been trenchantly critical of its approach to the deficit) it is difficult to argue that it has delivered weak government. That in itself is a powerful argument for the kind of electoral reform that would further erode the two-party bias in our politics. For both good and ill, this has been a revolutionary year in British politics. And 2011 promises more violent turns of the wheel.