Steve Richards: It's easy to talk about fairness – but hard to put into practice

Negotiations between the two Coalition parties over this month's Budget and in relation to some other important policy areas might as well be televised live in a studio.

Both sides make their moves in public and in some cases choose to do so in a studio. On the BBC's Today programme yesterday, Vince Cable told his interviewer that he would not negotiate what he wanted from the Budget on air. Cable then proceeded to outline his terms in considerable detail. If he secured a Mansion Tax from George Osborne he would accept the scrapping of the top rate of tax for high earners. Later in the day a letter from Cable to David Cameron on the need for more coherent and proactive policies on other fronts was leaked, or re-leaked as the contents of Cable's letter had already been reported. Public negotiation takes many forms and Cable is far from alone in his visible assertiveness.

On one level, the dance between the two parties is calmer than it seems, at least as far as the Budget is concerned. The Conservatives are also committed to exempting lower earners from income tax. The internal debate is about timing. There are no tensions over the principle. Similarly, while Osborne and his colleagues are keener to dump the top rate of tax than the Liberal Democrats, they also worry about the timing of that move. "We are all in this together" is Osborne's most famous slogan. A Budget that is seen as helping, above all, the highest earners would be politically risky. Osborne will need some very big protective shields in the form of help for the poor and the so-called squeezed middle in other measures before he acts.

The urgent need for both parties to be perceived as "fair" represents a sea change in British politics. At the height of the New Labour era, Tony Blair and Gordon Brown were too scared to raise the top rate of tax for high earners. Now David Cameron and Osborne are wary of dropping the high rate. In the late 1990s, policies for growth were hailed and redistribution carried out on the quiet. Now the Liberal Democrats, and to some extent the Conservative leadership, emphasise their support for some forms of redistribution. Fairness is the new political battleground.

The principle of fair taxes is much easier to espouse than the detailed policies. Vince Cable has advocated a Mansion Tax for several years. When he first put forward the policy he included properties worth a million pounds, only to discover that voters in quite a few marginal Liberal Democrat seats would be losers. Now homes worth two million are in his sights. He and others make the powerful point that property is easier to tax than income and some owners have made a fortune.

On the Today programme, Cable accepted that one way of implementing his favoured policy would be to introduce new council tax bands. I will be surprised if this specific measure gets the go ahead. A pre-election revaluation of properties would be a dangerous exercise in which all kinds of unexpected losers could surface. A fair objective can lead to some politically awkward outcomes. There are other ways of taxing soaring property values that would allow Cable and his party to claim a modest victory.

The Liberal Democrats are fighting for their political lives and the Conservatives want to win an overall majority at the election. Nowadays, economic policy is made all year around. The Budget is the moment when we pay most attention. For both parties the political message is as important as the substance. The unprecedented and not unhealthy public debate between ministers will get noisier as the Budget moves closer and even louder afterwards.