British politicians, commentators and the public like to believe in their sturdy autonomy. We have arrived at our decisions as freeborn men and women. We debate our ideas furiously in pubs, on radio phone-ins or via letters to the editor. We read the opinion pages. We elect a sovereign parliament that passes the laws and regulations that we mandate.

The truth is more subtle. We dance to another country's tune. It is the United States that makes the political, cultural and intellectual weather. It is the rich American institutes that develop the ideas for XYZ plan or ABC radical reform. Our academics, especially in the social sciences, want to get published in the American journals and ensure they please the editor in question. Our politicians watch closely to see what works in the US. We enjoy their movies and use their technology. The West Wing and Mad Men are part of our culture, as are Sex and the City and Friends. We think we are free; we are painfully and excessively influenced by the US.

Which is why the election of Barack Obama matters so much. In the tidal wave of tears of joy, analysis of county by county results, the "were you awake to hear the speech" conversations, naming the puppy and the critiques of Michelle's wardrobe - and yet another article on the big things in his in-tray - one thing has been underplayed. Obama's success will transform British politics. The centre ground will move significantly to the left.

No account of the rise of Thatcherism or the character of new Labour is possible without acknowledging the force and impact of the 30-year ascendancy of American neoconservatism. They won control of Washington in the late 1970s, creating the Washington consensus. No country - from communist China to the Nordic social democracies - held out. Everybody, to a degree, bought into the market fundamentalist consensus. Tony Blair could have held out more than he did - but the room for manoeuvre was tiny.

It went very deep. Editors of the top US social science journals published articles in this idiom because they had secured their jobs by conforming to it; ambitious British academics soon learned what was accepted and what was not. Young British investment bankers training in New York learned about the value of securitisation. Treasury officials on secondment to Washington bought into the consensus that privatisation and deregulation were the only ways forward. From social policy (remember zero tolerance and broken windows) to " light touch" financial regulation, and from a belief in labour market flexibility to distrust of public service broadcasting, the cultural and intellectual backdrop was conservative.

Obama's election ends that. American conservatism is now in profound disarray. It is not just that Republicanism has been forced back to the south and the mountain states: the intellectual paradigm that it championed led to nowhere but a credit crunch, a bloated and overpaid financial elite and the onset of a deep recession. No accident that Obama's lead jumped in the wake of the Lehman Brothers' bankruptcy and the part nationalisation of the banking system. Conservatism was on the ropes. A change had to come. Yes it did.

Here is a checklist of areas where the discourse is going to move left - intelligently and moderately because that is part of the Obama DNA. Firstly, trade unionism. Barack Obama shares the view of liberal Democrats that the best way to roll back the stagnating real incomes of the squeezed middle of the United States is to strengthen the bargaining power of organised labour. An empowered upper working class across all ethnic groups is the backbone of both the Democrat party and the economy.

This president is the most pro-union since Roosevelt. He wants to help unions organise and get recognition through a simple membership card check system, which workers can use freely and anonymously to signal their readiness to join - fiercely opposed by American business. This June, Obama even wrote to Tesco boss, Sir Terry Leahy, urging him to work with unions in the US (as he already does in the UK). The anti-unionism that led US officials to veto OECD reports that questioned labour market flexibility will be over. Now the US will encourage the OECD to publish evidence.

The BBC and Channel 4 should also be relieved at the victory. Obama is a strong supporter of public service broadcasting and caps on media ownership; he wants to see every American television and radio network commit to neutrality. In the US, one of the live issues is whether the Fairness Doctrine, requiring equal time between different points of view on broadcast media, should be reinstated - it was abolished by Ronald Reagan.

The subsequent avalanche of right-wing shock-jocks, the dumbing down of the American media and the partisanship of Fox News are even more an issue for the left in the US than the power of the right-wing print media is in Britain. For Democrats in the House, and Obama's chief of staff Rahm Emanuel, reinstating the Fairness Doctrine is of iconic importance. Obama may stop short of imposing a legal obligation on broadcasters - but he will go a long way towards it.

So it goes, too, with tax. This is the president who will redistribute income from the top 5 per cent earners above $200,000 to the other 95 per cent. There may not be much cash involved, but as Professor Avner Offer says in The Challenge of Affluence,, the point about higher tax rates is not so much the cash they raise but the signal they send about the dominant values of society. Obama has clear views on that. As he has on tax havens.

His reforms of Wall Street will be far-reaching; he will constrain bank bonuses, introduce tough new regulations and, as Roosevelt did, set up a wave of new banking institutions. He is already committed to a National Infrastructure Bank. When this is set up, financing roads, railways, bridges and dams across the US, the argument that Britain should have one too will become irresistible. Obama will try to deliver universal health provision. He will try to extend college access. He will want to build affordable homes. He will try radically to lower the US's carbon footprint, lower petrol consumption and improve energy efficiency. He will aim to reindustrialise the US.

As for foreign policy, he will be more multilateralist and there will be no Iraqs on his watch. But he is closer to Tony Blair and David Miliband (I think, rightly) as a liberal internationalist than many on the British left might like. Enlightenment values, democracy and human rights are worth asserting as universal rather than western principles. And, at the limit, worth fighting for. Trade is a big question mark. His party remains very protectionist.

For all that, the message is unmistakeable. Barack Obama will change the trajectory of the US.

I have found it odd to have been pro-BBC, pro-multilateralist Europe, pro-moderate trade unions, a City of London sceptic, pro-public service, pro-fairness and pro-redistribution for more years than I can remember. Now the leader of the world's hegemonic power, in control of its political, intellectual and cultural levers, is making this cluster of views the mainstream. The Labour Party and the wider liberal left are being given permission to be moderately and intelligently social democratic again. It may be a hackneyed phrase - but this really is a seminal moment.

Will Hutton is executive vice-chair of The Work Foundation