The proposals would extend the existing 0.5% stamp duty paid on shares to other financial assets, including bonds and derivatives, in a bid to create what Labour is calling a fairer tax system and to cut down on speculative computer-driven high frequency trading.

McDonnell said in a speech at the weekend: ‘The next Labour government will introduce a “Robin Hood Tax” to make the financial sector pay its fair share after it received huge public bailouts in the crash.

‘All we're asking for is fairness in our tax system. By making those who trade in financial derivatives pay a small fraction of their profits, we can help properly fund our public services.’

The concept of a financial transactions tax has been under discussion within the EU for several years, and has proved highly controversial. The European Commission first put forward the idea in 2011 but the plans ran into stiff opposition, not least from the UK, over concerns about the impact on City of London and other financial trading centres.

Subsequently a smaller group of member states went ahead with exploring the concept, under the EU’s ‘enhanced cooperation’ rules, which require consensus from at least nine countries. Austria, Belgium, France, Germany, Greece, Italy, Portugal, Slovakia, Slovenia and Spain are still discussing the options, while Estonia left the project in 2015.  There have been considerable delays over any announcement on progress and possible outcomes.

Labour’s latest briefing suggests the financial transactions tax would have raised £4.7bn in 2017 before rising to £5.6bn in 2022. However, the plans have been criticised by a number of think tanks and business organisations, on the grounds they would damage the UK’s pre-eminent position in financial services, and would also drive up costs.

Julian Jessop, chief economist at the Institute of Economic Affairs, said: ‘It’s naïve to think that the burden of financial transactions taxes will only fall on banks and speculators. The increased costs would inevitably be passed on to customers, including small investors, in the form of higher charges, and to borrowers in the form of higher interest rates. Non-financial firms will find it more expensive to raise capital and manage risk, which will undermine the economy further.

‘Indeed, this is another example of the fallacy that corporations can be tapped for cash with no wider costs. In reality, it’s always ordinary people who ultimately pay, including consumers and workers. Sherwood Forest wasn’t made of magic money trees either.’

The Labour party has also indicated plans for ‘the biggest crackdown in this country's history’ on tax avoidance, which would include action on shell companies and offshore tax havens used to hide wealth. In addition, those earning more than £1m would be required to make public their tax return information.

Jessop said: ‘Labour’s promise to crack down on tax dodgers is a good soundbite and it’s surely right that companies and individuals should pay what is due.

‘But successive governments have made similar commitments and it’s unclear that Labour’s proposals are a major step forward.

‘Their promise also needs to be set against their plans for large increases in the tax rates payable by large corporations and higher earners. These could actually worsen the problems of tax evasion and avoidance by increasing the incentive to game the system.’