The Labour party has, among other things, suggested that the UK introduce a financial transaction tax to raise a whopping £26 billion. The idea has been around for some time and there are existing pressure groups set up to push for such a levy. The EU has been considering how to introduce a such a tax, although Member States have found it hard to agree on the specifics. However, the UK has had a well-designed financial transaction tax for over a century – it’s called stamp duty.

The idea of a financial transaction tax was originally put forward back in the 1970s by the Nobel-Prize-winning economist James Tobin, which is why it is sometimes called a Tobin Tax. He envisaged it as a levy charged every time one currency was exchanged for another. The idea has since been extended to other sorts of financial trading. The EU financial transaction tax would require a small amount to be paid over to the authorities each time a share or a bond is sold. The amount is a sliver of the price of product, somewhere between 0.1% and 1%. More ambitious versions of the tax would also tax exotic financial instruments called derivatives. Such is the enormous volume of trading in today’s financial markets, even very low rates could lead to a substantial tax take.

Campaigners have dubbed the financial transaction tax the “Robin Hood” tax because they imagine it would be paid by rich bankers and the proceeds given to the poor. James Tobin suggested the money raised should be given to developing nations. Certainly, a Robin Hood tax sounds appealing on social justice grounds. But sadly things are not that simple. Yes, a financial transaction tax would primarily be paid by banks, but they would simply pass this cost on to their customers. So a Tobin tax would not be borne by bankers. The people who would end up paying are bank customers like you and me.

However, noting that financial transaction taxes are paid by ordinary people is not in itself an argument against them. All taxes are paid by people, it is just that some are better concealed than others. There are strong political arguments for taxes that we don’t notice since we are less likely to complain about them. The argument that a financial transaction tax would be suffered by banks in a convenient fiction for a government that desperately needs to raise more money.

So, a financial transaction tax with a low rate might be a good idea to raise revenue. It is a potential small tax that, if set at the right level, few people will notice. But you have to be careful. Bond traders don’t have to operate in London, Paris or Frankfurt. They can trade from the beaches of the Caribbean or the bars of Hong Kong or their living rooms in Sydney. When Sweden brought in a tax on selling bonds in 1989, with a rate of just 0.003%, the number of transactions fell by 85% in the first week. The tax ended up raising less than a tenth of what was expected and was scrapped in little more than a year. If the EU imposed a Tobin tax, financial traders might gradually drift away to more welcoming shores.

Likewise, the effect on the City of London of the UK unilaterally introducing a financial transaction tax would be catastrophic. That’s why the British government opposed the EU’s plans for such a tax unless the rest of the world were to implement one too. This is sensible. Since a vast amount of business is done through London, the British exchequer would be a major beneficiary of an international tax. But it would have to apply everywhere, or any country that didn’t implement it would quickly steal London’s financial pre-eminence. These objections meant that, even before Brexit, the UK was not part of the plans for an EU financial transaction tax. Even the countries that are interested in taking part are finding it very hard to agree exactly how it should work.

Luckily, there are some financial instruments that are not as mobile as bonds and derivatives. If you want to own shares in a listed UK company, almost the only place you can buy them is on the London Stock Exchange. Admittedly, there are special financial products called depositary receipts that can be traded in other countries and some companies, like Shell and HSBC, have dual-listings in more than one country for historical reasons. But generally speaking, UK shares have to be bought and sold in London. Since it is impractical to buy UK shares anywhere but in the UK, the government can tax share sales without worrying about all the business moving elsewhere. For many years, selling UK shares has been subject to a special levy called stamp duty reserve tax. This is collected automatically by the electronic settlement system of the London Stock Exchange. The rate is 0.5% of the price of the shares.

This means there is hope for a slimmed-down version of the European financial transaction tax if it is restricted to shares. Both France and Italy have jumped the EU gun and enacted their own version of the UK’s stamp duty, and Spain and Portugal have plans to do the same. Since quoted French and Italian shares are traded at the Bourse de Paris and Milan’s Borsa Italiana respectively, these provide a captive market that governments can trim. Basically, other European countries are adopting the system that the UK has had for decades. When introducing new taxes, copying a successful model from elsewhere in the world is often a good idea.

Stamp duty includes various exemptions that prevent the market from seizing up. There is no reason that a more general financial transaction tax should not work just as well and raise lots of money. The fundamental problem remains that the market would move to avoid the tax, which means it would have to be introduced everywhere at the same time. Since that is not going to happen, the Robin Hood tax is one of those good ideas that will never happen.

James Hannam is the author of What Everyone Needs to Know about Tax (Wiley, 2017).