Chris Rokos is moving his tax residency from the UK to Greece. He paid around £330m in UK tax last year and was the third largest individual taxpayer in the country. Greece will charge him a flat €100,000 a year on his foreign income for up to 15 years.

In July, 120 UK millionaires wrote to the new prime minister under the banner "tax us, we're proud to pay and here to stay." They want 2% a year on wealth over £10m.

What is striking is that on combined wealth of perhaps £2-£3bn, this group probably pay somewhere between £40-£80m of tax a year. Rokos on his own pays four to eight times that.

Hasn't the wealth tax question already been answered?

In 2020 the Wealth Tax Commission, comprising eminent experts including Arun Advani of Warwick, Andy Summers of the LSE and Emma Chamberlain of Pump Court Tax Chambers spent a year studying how wealth taxes work in seven other countries. It is the most serious work Britain has done on this subject.

They rejected the idea of an annual wealth tax. They said it would be too costly to administer relative to what it raises and too exposed to behavioural response. The tension nobody has solved when it comes to a wealth tax is this: the base must be comprehensive to prevent avoidance, but revaluing private businesses every single year is the hardest job in the tax code. What the Commission recommended instead was a one-off levy fixed at a past date, which cannot be escaped by emigrating, alongside structural reform of the wealth taxes we already have.

Their modelling put an annual wealth tax at 0.17% above £500,000 at roughly £10bn, before administrative costs. The patriotic millionaires say 2% above £10m delivers £24bn - clearly a different answer.

What the campaign placard leaves out

I do tax for a living and see a number of practical problems with an annual wealth tax.

  • Valuation. Listed shares are easy. Try valuing 500,000 private trading companies, farmland, development land, goodwill, art and plants every year. HMRC has no asset register and no capacity to build one. The reliable output is not revenue, it is disputes.
    The answer I keep hearing is that assets get valued in divorce, so clearly it can be done. But ask anyone who has been through one. It takes years, each side instructs its own expert, the two numbers come back miles apart, and a serious share of what is being argued over is spent arguing over it. That is what valuing private wealth looks like when it is done once, with a judge at the end to stop the argument. A wealth tax would need it every year, for hundreds of thousands of people, with no judge and no transaction.
  • Liquidity. Income tax follows a transaction, so there is cash to pay it from. A wealth tax follows a valuation, so frequently there is not. The founder of an unquoted business with an £80m paper value and no dividend has to sell something. Usually equity. Usually to a buyer overseas.
  • Mobility. The charge falls hardest on the most liquid and most portable wealth, held by the people best placed to leave. The person who cannot leave owns a factory in Rotherham. The tax selects, with some precision, for the wrong outcome.

What I would do instead

Some say if one rich man's departure can markedly dent public finances, that is an argument for a broader tax base. But surely it makes sense to broaden towards what cannot move, rather than accelerating the departure of what can. Here I mean land and wealth.

A land value tax, offset by scrapping stamp duty would in my opinion be a good alternative solution. Yes, that needs valuation too. But land is visible, already mapped, and valued plot by plot rather than as a shifting minority stake in a trading company. Nobody has yet flown a field to Athens. Achieving this would however be slow, unglamorous, cross-party work, which is presumably why nobody is holding a placard for it.

Politically some are making the argument the rich should pay more. Others are highlighting capital risk. The answer in fact is that we need a tax instrument that actually works.

Andy Oury is an owner partner at Oury Clark Chartered Accountants