The revelations in the Paradise Papers leak have showed, once again, that our economy is rigged to the benefit of the powerful, the wealthy and giant corporations. While most of us are expected to – and do – pay the taxes that are due from us, a tiny minority operate under different rules. If you’re rich enough, you can join the same exclusive club – a world of offshore trusts and secretive tax havens, administered by offshore specialists like Appleby’s, the firm at the centre of current revelations. It is one rule for the super-rich and another for the rest of us.

Paradise Papers: Theresa May refuses to promise register of offshore trusts Read more

What the 13.4m documents that comprise the Paradise Papers show, like the Panama Papers before them, is the sheer extent of offshore tax avoidance. The problem is endemic to the global financial system, and Britain is at the centre of it. Investigations over the summer revealed that more than £1 in every £7 that corporations placed in tax havens came through the UK – making it, with the Netherlands, the largest single conduit for corporate avoidance by some distance. Our historical connections to notorious tax havens such as Bermuda and the Channel Islands, along with the City of London’s massive financial infrastructure, make Britain an ideal sluice for finances seeking secrecy and dodging taxes.

This is not about a few individuals seeking to undermine the system, it is the system. It developed over decades, and ending the unfairness of it will require the serious, systematic efforts from committed governments here and across the world. Thanks to its historical links, Britain is uniquely placed to help end the scourge of tax avoidance, freeing up resources for essential public services like the NHS after years of grinding Tory spending cuts. Labour is absolutely committed to stamping out tax avoidance once and for all. We announced before the election the most comprehensive anti-avoidance programme ever published by a major political party in Britain and are pushing this government hard on the issue.

The Tories have attempted some of the same rhetoric. David Cameron called tax avoidance “morally wrong”. His chancellor, George Osborne, called tax avoiders “leeches on society”. Prime Minister Theresa May said companies have a “duty” and “responsibility” to pay their taxes.

But at every step of the way, whatever fine words are said in public, Tory governments consistently seek to undermine and reverse efforts to clamp down on tax dodging.

Play Video 2:18 Lord Ashcroft hides in toilets to avoid questions on tax – video

HMRC set up a specialist unit to investigate “high net worth individuals” in 2009. When the House of Commons public accounts committee examined the unit earlier this year, they discovered it was today bringing in £1bn less than when it was set up. The same report found that of the 72 investigations into wealthy individuals opened by HMRC in the five years to 2016, only one resulted in a prosecution. HMRC has been woefully under-resourced by this government, losing 40% of its staff in a decade.

Tory failure has antagonised our closest international partners. The European parliament has directly criticised this government for obstructing the fight against money-laundering, tax evasion and tax avoidance, with Tory MEPs repeatedly seeking to block anti-avoidance measures. Osborne’s changes to the “controlled foreign company” regime – allowing multinationals a further tax loophole through which to funnel funds – has been placed under investigation by the European commission.

Despite promises made by David Cameron as far back as 2013 – and despite her rhetoric upon becoming prime minister – Theresa May is today pointedly refusing to back a full, public register of offshore companies and trusts. Campaigners have demanded this as an essential step towards shining a light on the activities of tax dodgers and the structures they exploit. Yet successive Conservative ministers have now spent four years rowing back from Cameron’s promise.

This year’s finance bill contained important amendments, tabled by Labour, to secure full transparency for offshore trusts. But the Tories voted them down, and preferred instead to keep protections in place for the ludicrous, anachronistic “non-dom” tax status that means someone born, living, and working here need never pay the full rate of tax.

Again and again, the Tories have failed to act on avoidance and have blocked the efforts of others. The only person who seems to believe the Tories are serious about tackling avoidance is Theresa May, who vainly clings to her “impossible to corroborate” figure for extra taxes collected by her government. Yet her own senior colleagues and associates now have serious questions to answer after the Paradise Papers revelations.

Paradise Papers leak reveals secrets of the world elite's hidden wealth Read more

Lord Ashcroft is a former deputy chair of the Conservative party and one of the Tories’ biggest donors, reportedly handing over half a million pounds to the Conservatives for this year’s general election campaign. He let it be known, as a condition of receiving his peerage, that he had given up his non-dom status. But he is named in the Paradise Papers as receiving $200m from his offshore trust in the tax haven of Bermuda.

Was Lord Ashcroft subject to proper due diligence checks before his donation was accepted by the Tories? Can the Conservatives assure us that he was paying taxes on his considerable wealth while he was a major donor to the Tory party? HMRC needs to investigate the amount of tax paid by Lord Ashcroft, and clarify his non-dom status. But beyond that we need a full public inquiry into aggressive tax avoidance and UK companies’ and individuals’ role in it.

There is the faint smell of venality hanging over this affair and this government that will only be cleared by a credible investigation through a public inquiry. But if this government is not prepared to take the action needed to end the scourge of tax avoidance, it must step aside for a Labour government that will.

• John McDonnell MP is shadow chancellor of the exchequer