The Nigella question taxes Gordon and Dave

The nation's foremost cupcake siren reveals that she does not intend to let her two children (by a previous marriage) inherit her fortune and that they should learn "that you have to work in order to earn money". Her husband, Charles Saatchi, disagrees and cannot see why he should not bequeath his own hard-earned assets to his offspring.

It would be interesting to hear whether the former Chancellor Lord Lawson agrees with this self-denial. Is he about to cut his daughter out of the family will at her request? The Saatchi-Lawsons will just have to sort it out between them.

Their differences reflect one of the oldest debates in politics - that between those who believe wealth should be recreated by each generation anew and those who see continuity, pleasure and justice in handing it down from one generation to the next.

When David Cameron and George Osborne launched a rescue bid for the faltering New Conservatism at their conference last autumn with inheritance tax proposals to give exemption of up to a million pounds on estates, the effect was instant political Viagra. The after-effect on the body politic is still being absorbed.

No single decision has had such a dramatic effect on a party's fortunes in recent memory. It changed the terms of trade with Labour by putting the party on the defensive in the face of a Tory advance - which is where is has stayed ever since. The impact on Labour's confidence even now cannot be overstated. " It was the ' Oh my God' moment," says one senior Cabinet figure, shuddering at the memory. "It swept away all thought of an instant election like a Harry Potter spell."

It also forced the new Chancellor, Alistair Darling, to offer an instant "next best thing" rise in IHT allowances to £700,000 for a couple. Even the Lib-Dems quietly raised their proposed threshold to £500,000.

Relatively little attention has been given to considering whether the IHT cut is good economics - or indeed a good thing as a whole, other than as a bargaining chip for votes.

The argument in favour of heavily taxing inherited wealth is an old one: and not just of the Left. It runs from the philanthropist Andrew Carnegie to Adam Smith in The Wealth of Nations (which Mr Osborne professes to be one of his favourite works of political philosophy - apart from this particular chapter, evidently.)

Smith's heirs on the economic Right today agree with the principle, notably Irwin Stelzer, who is close to Rupert Murdoch and thus of rather special interest to political leaders.

Mr Stelzer complained recently that the main parties had "abandoned the laudable goal of making opportunity more equal for all to favour the beneficiaries of six per cent of estates that pay inheritance tax: a terrible tradeoff ". The proceeds of inheritance tax tend to go into subsidising the children of the well-off to work less - or one partner to stay at home, which sounds very pleasant but, as he points out, is not what countries locked in an ever-fiercer battle with overseas competitors should seek to promote.

Hopes that IHT cuts could be balanced by cuts to taxes for the lower-paid or small businesses are fading, since, as the Institute for Fiscal Studies shows in its projected 2008 "budget", there is precious little slack on spending at all - and the election contenders are more likely to be struggling to make ends meet than splashing money about in tax cuts.

How the state views our assets tells us a lot about the preoccupations of the times. Lady Bracknell bemoans that Gladstone's death duties on landed estates "give one position but prevent one from keeping it up". Attlee's swingeing inheritance taxes on the rich set off fears of punitive taxation which haunted Labour thereafter.

But isn't Ms Lawson correct in advocating that we should all make our own way? Theoretically, yes. Practically, not so easy. Absolute opposition to passing on wealth tends to be the preserve of socialists on the one hand and the very well-off and socially super-confident on the other. Bill Gates is another example of this spartan entrepreneurial breed.

It is worth reminding purists like Mr Stelzer and Ms Lawson that people feel so resentful about inheritance tax today because it affects the salariat far more than the independently wealthy, who can easily put money beyond the taxman's reach. The anxious middle classes are also far more likely to worry that their children will end up poorer than they were than that they will be too spoilt to achieve. Besides which, they have already paid out once in taxation on income - and, these days, in involuntary extras for their young such as tuition fees, too.

Modern politicians know that tax is about aspiration as well as circumstances, and accurately calculating the gap between the two. So Labour strategists believe that their £700,000 IHT ceiling will satisfy voters that they will not end up in a tax trap linked to rising property values. They see no need to give money back to the top one per cent of earners who have homes valued at more than £1 million - and indeed believe more of us will resent the Conservatives' largesse here than support it.

Mr Osborne has the counteradvantage of having come up with a memorable sum to underline his party's claim to better understand and support those who hope to climb the prosperity ladder. He will struggle to show that he can really raise enough money from taxing non-doms to pay for his generous plans. But Labour's margins are not exactly comfortable here, either. Remember Mr Brown ruled out raising IHT thresholds in his last budget as Chancellor. Now he is committed to doing exactly that, even though the public finances look worse, not better.

The "Nigella question" reminds us that the age-old business of inheritance is back in the fray as the parties stake out their electoral territory. How cheering that the next big tax giveaway is the one we'll have to wait till we're dead to get.