Hurricane Maria is fast approaching the British territory of Turks and Caicos, while thousands of people in British overseas territories continue to struggle with Hurricane Irma’s fallout. They have yet to hear the government’s long-term plan to provide the support and funds they will need to rebuild their communities.

These are national disasters in British territories, but the government is not living up to its responsibility for dealing with the outcomes, as it would for a disaster on British soil.

The Tories found £1bn for the DUP. But for those who have had their homes destroyed and their world turned upside down, resources are supposedly scanty.

The government should be finding seed funding from across Whitehall and using it to leverage extra private investment. And it should finally be helping these territories to diversify their economies away from tax havens for corporations and the super-rich. Instead, Boris Johnson and Theresa May chose last week to use this opportunity to once again attack the UK’s aid budget. They said they were frustrated that Britain cannot spend aid ringfenced for the poorest countries on wealthier British overseas territories.

The foreign secretary and prime minister know that repurposing the 0.7% of our gross national income that we spend on official development assistance (ODA) towards British territories would have a detrimental impact. It would divert crucial aid that is currently saving millions of lives in conflict and crisis situations, helping millions of children attend school, combatting curable diseases and tackling gender-based violence.

Their proposal would take vital support away from some of the world’s most vulnerable and deprived people, and threaten the stability of some of the most fragile countries. And it would undermine international development assistance as we know it, subverting its central principle to support the world’s poorest countries. It would make a mockery of the UK’s hard-earned reputation as a global leader in international development.

The right-wing media and Tory politicians peddle the myth that the ODA rules defy common sense, imposed on us by international institutions. But these rules are robust. They make sure aid goes where it’s most needed and that citizens in donor countries can trust that their taxes aren’t being misused. The rules have been agreed internationally and updated over many years, and are based on experience of what works. And the UK, as a significant global donor, has played a key role in shaping what they look like.

This week Guy Hewitt, the Barbados high commissioner, reminded us that international development assistance is far from perfect, and that more support is needed for small islands. But this is very different from the dangerous argument put forward by Johnson and May.

They know that ripping up the rulebook is a promise they can’t deliver. As for Priti Patel, the secretary of state for international development has never actually articulated what specifically she disagrees with in the existing rules, or what she would seek to change.

The government must rule out lobbying for development assistance to be spent on wealthy countries or in British territory. Instead of treating Irma and aid rules as political footballs and making more promises to the British public that can’t be kept, it is time to get on with the business of governing properly: they must present an ambitious, resourced plan for the overseas territories’ recovery, but without re-purposing ODA.

Last week we heard harrowing accounts from people in Anguilla and the British Virgin Islands asking where the support was from the British government – a government that has the responsibility for protecting these territories.

As Hurricane Maria starts to hit British territories, and will possibly affect the same, already battered, countries, the government must quickly go beyond the initial emergency response and find the long-term resources needed – without threatening to take it away from the poorest and most vulnerable parts of the world.

Labour has promised to fight for the spirit, as well as the letter, of our 0.7% pledge, and we will continue to do so. If the Tories abandon the essence of that pledge, history will judge them accordingly.

• Kate Osamor is shadow secretary of state for international development