Talk is cheap in the clampdown on tax avoidance First it was Google; then Amazon. This week it was the turn - again - of Apple to be the latest big international company to come under fire for adroit tax planning. The tech group chose to pay money back to shareholders by raising $17bn of debt rather than repatriate some of the huge reserves of cash it holds overseas, which would have resulted in it writing a big cheque to the US Internal Revenue Service. The move has stoked the growing concern over corporate tax planning. As a financial crisis became a fiscal crisis and then a political crisis, public anger has risen over a flawed international system that allows billions of dollars, pounds and euros of profits to go untaxed. Politicians have read the mood, raising their rhetoric to condemn big tax avoiders and what David Cameron, UK prime minister, described as "the travelling caravan of lawyers, accountants and financial gurus." At a time of austerity, nobody wants to be seen as soft on tax avoiders. The tax planners have taken note. At an Asia-Pacific tax summit in Shanghai last month, KPMG accountants discussed "evolving attitudes toward tax morality." "The whole atmosphere is changing," says one chief executive who has, for years, driven down his company's tax rate. Tax avoidance is no longer acceptable. Politicians are playing a dangerous game, however. Governments are complicit in the problems they are condemning. It is their tax systems that have created incentives for businesses to behave in this way. Moreover, fuelling public anger over how big companies play the system - not always justified - may well encourage non-compliance from those who feel that "everyone is at it." Only real reforms can deal with the problem - and the prospects of that are far from certain. The global effort to plug leaks in the tax system has been led by the OECD, the group of mainly rich nations. But it can only advise. At the latest G20 meeting, Angel Gurría, secretary-general of the Paris-based body, told political leaders that it was really up to them. Let me be blunt about this. A meaningful action plan cannot be delivered by June unless you express strong political support. And there lies the problem. Agreeing a radical new set of rules would create winners and losers, both of which must agree to any new deal. Countries want to protect their own interests. Tax is at the heart of national sovereignty - and is thus fiercely defended. The proposal for "unitary taxation" - an idea popular with campaigners and academics - is a case in point. Under this system a company's taxable profits would be carved up according to where it does business. But critics say this would favour countries with expensive property and high salaries; many wary treasuries have given the idea the thumbs down. Even milder reforms - such as tweaking the way in which royalties on things such as intellectual property or brands and knowhow are collected - would be tough to realise. Those who benefit from current arrangements oppose any changes. That is why, instead of fighting over how to divide the existing cake, policy makers are focusing their efforts on working out how to increase its size. They are aiming their fire on "double non-taxation," the gaps in the messy, overlapping international tax rules that allow tens of billions in revenues to escape taxation altogether in any country. Tackling these gaps, they argue, would reinforce, not undermine, national sovereignty over tax. Here attention inevitably turns to tax havens. Big developed countries have for years been ambivalent - perhaps even two-faced - about them. For all the fiery rhetoric about "fiscal paradises," there has also been a view that they can sometimes play a useful role as a pressure valve, allowing governments to attract international investment without having to lower tax rates at home. Also, the most significant havens are not the tiny islands with pristine beaches and zero tax rates that can be bullied into reform. Offshore-style tax-dodging occurs in many large "onshore" countries, including powerful countries at the heart of Europe, where mismatches between different regimes can create opportunities for lucrative savings. These quirks are one reason why so much money - hundreds of billions of euros - flows through companies in apparently high-tax countries such as Luxembourg and the Netherlands, attracting little tax as it goes. There are ways to tackle this. For instance, governments could stop companies deducting interest from a tax bill if they knew that this was ultimately destined to be transferred to a jurisdiction where it would not be taxed. The good news is that changes of this sort could happen. The EU and OECD are pushing hard on this. While it would be an achievement, don't hold your breath: it would still not amount to the radical reforms that critics say are necessary. The role of the US is also critical. America's tax code has not really changed for more than a quarter of a century. In that time scores of anomalies and excesses have built up, often with bizarre consequences - as the Apple example shows. If the US does overhaul its tax code - introducing a meaningful cut in rates, say - the effects would ripple across the world. One consequence could be more tax competition. This could exacerbate some of the current problems. Already, many countries" instincts are to compete, not co-operate. The desire to collect more tax at the same time as using fiscal competition to gain advantage may be inconsistent but it is a strong one that is very difficult to resist. The tax-planning gymnastics displayed by Apple this week may be a powerful reminder of the need for reform. But unless there is a change of heart among policy makers, a meaningful crackdown on avoidance is not going to get far.