John McTernan: Fairness for all is not an easy task

'It's not fair." The cry rings out in playgrounds across the country. And, if we're honest, in our homes and offices as we compare our lot to the "undeserving" ones who have pushed ahead of us into better jobs, schools or houses. Well, we're going to hear a lot more about fairness in the coming months.

Over the party conference season it has been clear that fairness is the metric by which our leading politicians have chosen to be judged. Whether it is Nick Clegg arguing that it's not fair to leave a huge debt for our children to pay off. Or Ed Miliband saying he'll stand up for the "squeezed middle". Or George Osborne and David Cameron defending cuts in the "middle-class welfare state" because "we're all in it together".

In each case there is an appeal to the fundamental fairness or unfairness of policies.

How did this slippery and often vague concept come to be at the centre of our politics? For Labour it's simple. Gordon Brown and Tony Blair adopted "fairness" so that they didn't have to use the term "equality". They feared that term smacked far too much of Old Labour - indeed, socialism - and made Middle England fear that they would have something taken from them to be given to others. This was such a successful political ploy that Cameron, when detoxifying the Tory brand, willingly embraced the term "fair" as the measure of how he would govern.

There is a conspiracy to between Right and Left to deny it, but the emergence of a "progressive conservatism" is a major sign of just how far to the Left the Labour government dragged the centre-ground of British politics, at least in social terms. And Nick Clegg? His instinct has always been towards economic liberalism - hence his ease in the coalition. The badge of "fairness" is an attempt to balance a move to the Right on economic issues with a progressive social outcome.

So there are clear reasons why the concept is so contested. But does it actually mean anything? Consider yesterday's row about the Browne Review of funding higher education in England. This is an argument about competing claims of fairness. Crudely, should those who directly benefit from a service - the graduates whose incomes will rise because of their degree - pay for it? Or should those who indirectly benefit - the taxpayer who sees the economy grow, or is treated by a British-educated doctor - foot the bill?

A different take on fairness was evident in the row at Tory conference about child benefit.Is it fair that a non-working mother with a parent earning over 44,000 loses her benefit while two working parents on a combined income of 86,000 would keep theirs? And then there's the rumbling row about immigration that flared in the election when Brown infamously called Gillian Duffy "bigoted". Talk to MPs of any party and they'll tell you this remains a raging doorstep issue where it is framed in terms of access to health, schools and social housing; in other words, "fair" access to public services, particularly scarce or rationed ones.

Is there a rigorous and robust concept of "fairness" that is flexible enough to connect all these debates?

First, there's a fundamental "contributory" principle - what you get out should reflect what you put in. The hard end of this debate is about social housing. How should you earn the right to move up the housing ladder? Most ordinary people think you should join the queue and wait your turn; being in a place, working there, growing up, bringing up your family, is your contribution.

That is, unfortunately, at odds with homelessness legislation across the UK which says that if you are homeless you will be housed before people who have been waiting longer than you. In other words, need trumps contribution. There would - in this analysis - be far less objection to migration if migrants didn't access welfare until they had worked for, say, five years.

Harsh? Yes. But fair? Certainly, if you believe that public consent for welfare institutions is central to a sense of social solidarity.

Second, there's the argument of fairness across the life-cycle. Child benefit is a modest recognition by the state that having a child is costly, yet the country wants families to have children. No redistribution can fully compensate parents for the cost of bringing up their kids, nor indeed should it, but it feels fair that you get some help when your finances are pressed. And, of course, higher earners, who pay more than half of all income tax, will more than recompense the taxpayer for the small support they receive.

Finally, there is fairness about the broadest shoulders bearing the greatest burden. In a sense it is there in the dispute about child benefit - working households with children, even if they are higher-rate taxpayers, feel more pressed than working households without them. In effect, they are arguing that they have higher needs which should be weighed in the balance.

But the financing of higher education is the best test case. It is true that a graduate has a premium on their earnings of at least 100,000 over a lifetime compared to non-graduates. So, it's fair that they should pay something back. And to prevent poorer students avoiding university because of fear of debt, it seems fair too to avoid upfront payments, and to get people to pay back out of later earnings. But the 100,000 premium is an average - some who become tax lawyers, or City brokers, earn far more.Shouldn't the high-fliers pay back more? From this principle comes the argument in favour of a graduate tax.

So, on the face of it, fairness looks simple. But as Ronald Reagan used to say: "It is simple, but it's not easy". Why? Well, balancing these different strands of opinion is like playing four-dimensional chess. Just as you move to restrict entitlement to welfare from "outsiders", people say "what about the children?". You move on the higher paid and they say "what about the stay-at-home mums". Finally, you go for the single, young person, and they protest too.

Traditionally, fairness, like taxation, is like the art of doing the most while attracting the least attention. In the next decade that will not be possible. It is the inescapable centre of our politics.