In any discussion about tax-dodging, the same old images crop up: squeezing a balloon, pumping a punctured tyre, playing whack-a-mole. Three different ways to express the single frustration in tax policy, which is that the system as a whole is only as strong as its weakest link. Leave the smallest crack for funds to sneak through, and an entire industry – international, ingenious and utterly ruthless – stands ready to funnel them through. The shell companies and border-sprawling organograms unearthed in the Panamanian vaults of Mossack Fonseca are a prompt to reflect on this old insight anew.

There are implications for finance ministers when they make decisions alone, and more especially when it comes to them acting together. They struggle to grasp either. On the home front, the “mind the gap” principle points to keeping taxes as simple as possible, with as few deductible allowances as fairness permits, and the smallest number of rates compatible with ensuring that the rich pay the biggest bills. Give any advantage to one form of remuneration or investment over another, and the tax industry will expend enormous effort on the socially wasteful but individually enriching business of making one thing look like another. Sadly, chancellors after a budget-day headline can rarely resist the temptation to unveil complex new perks.

It is not leftwing to worry that complexity allows avoidance. It was no socialist but Nigel Lawson who aligned the taxation of capital gains and higher incomes, because he understood that any difference between the two amounted to an invitation to executives to pay themselves in share options, rather than salaries. Sadly, George Osborne doesn’t understand this – or chooses not to care – and slashed the rate of capital gains tax last month.

Within each country and internationally too, the aim must always be to tax different vehicles consistently, minimising the rewards for shape-shifting schemes. The failure to understand – or care – about this was one of the depressing things about David Cameron’s letter to the EU, calling on it to go easy on rules about the transparency of trusts at the very same time as he was making fine noises about openness for companies. Any such difference in treatment will inspire rich individuals to play metamorphosis with their wealth.

The ultimate safeguard against dodging would be to harmonise taxes across national borders, but the political obstacles are significant. The first step, which really should not be so difficult, is to agree to consistent transparency. This week, in direct response to the Panama Papers, Britain’s man in Brussels, Jonathan Hill, signalled that plans for country-by-country corporate reporting within the EU would now be extended to cover tax havens too. That sounded like real progress, but – on inspecting the plans – it took the experts no time to find vulnerabilities. Away from the EU and named havens, the rest of the world will remain as a black box, with companies remaining free to conceal information they already collect on their earnings in most states. Worse, the new requirements for havens only apply to those given that designation by the EU on narrow criteria, which exclude several major centres of offshore activity.

In Brussels and in London, then, those writing the rules continue to fall short of the comprehensive approach that is required. The upshot is that they are still whacking moles. And it leaves them ripe, too, for a familiar verdict from another game: you are the weakest link.