The UK government has been accused of breaking its promise to double financial support to poor countries to help tackle climate change.

Climate and aid organisations said the government’s “devastating” foreign aid cuts make its pledge to spend £11.6bn on international climate finance by 2025 “very questionable”.

They warned the proposed £4bn cuts have also “weakened the UK’s moral position” to encourage other nations to increase their climate funding targets ahead of November’s United Nations COP26 climate conference, which the UK is chairing.

It comes as MPs demand a vote on foreign aid cuts in Parliament, with prominent Tory backbenchers like Theresa May and Andrew Mitchell calling for the government to reverse the plans.

Rebel MPs failed to secure a vote earlier this week, but the speaker, Lindsay Hoyle, called on the government to give the Commons “the respect it deserves” by granting an “effective” vote.

Now, in light of the foreign aid cuts, senior international development figures have cast doubt over the validity of Boris Johnson’s pledges about climate finance contributions.

The prime minister is hoping to use the G7 summit in Cornwall, which starts on 11 June, to “secure a substantial pile of cash” in climate finance commitments from member states. He even phoned his German counterpart Angela Merkel last month, imploring her to follow the UK's lead by increasing its contributions, despite Germany already giving significantly more than the UK.

But experts have now accused the government of “giving with one hand and taking with the other”.

Andrew Norton, director of the International Institute for Environment and Development, told openDemocracy: “There is a real problem about cutting the aid budget and still making the claim that you're delivering on the £11.6bn,” he said.

“If you're reducing your development spend, then it's very, very questionable whether you can count climate finance as new and additional.”

In 2019, Johnson announced that the government would double its spending on climate finance to £11.6bn over the next five years. But the following year it announced a reduction to its foreign aid budget, from the internationally backed level of 0.7% of gross national income to just 0.5% – a cut of £4bn – in response to the financial impact of the pandemic.

Oxfam’s senior climate adviser, Tracy Carty, said that by increasing climate finance from a declining aid budget the UK government was “giving with one hand and taking with the other”.

“Supporting the countries on the front lines of climate change should not be at the expense of vaccinating children against deadly diseases, building hospitals or providing communities with clean water,” she added.

Climate finance is intended to help poor countries reduce their greenhouse emissions, through investment in clean energy generation, for example, as well as helping them to cope with the effects of climate change, such as floods and droughts.

In 2009, the UK and other wealthy countries promised to scale up climate finance to $100bn a year by 2020 and agreed that this money should be “new and additional” to what they already spend on aid.

The commitment was intended to prevent governments from reallocating funds from their existing development budgets to pay for climate action, which “lets advanced economies off the hook for these two different responsibilities,” explained Katie Gallogly-Swan, who works on climate policy with the United Nations Conference on Trade and Development.

In a 2018 climate report, the British government told the UN it defines climate finance as “a new, dedicated climate commitment which is additional to historic official development assistance levels and has not diverted funds from existing development spending.”

Former senior UN officials said the UK was now appearing to go back on its word. “Promises made should be promises kept,” said Rachel Kyte, a top World Bank official at the 2015 Paris climate conference.

“Climate finance promises haven’t been and should be before COP26 later this year. This means making good on the level of commitment indicated and showing how this will be increased for the period to come.”

Last year, the UN secretary general António Guterres said that rich countries had failed to meet the $100bn climate finance target they set in 2009. Aid organisations warned that by cutting foreign aid, the UK is jeopardising efforts to get other countries to up their commitments at a time when they are failing short.

“The UK aid cuts are already having a devastating impact on people who live in poverty and those most impacted by climate change, especially women and girls,” said Francesca Rhodes, a senior policy adviser at CARE International UK.

Many climate experts believe the current climate finance targets are already too low. “It's common knowledge that that $100bn goal is a farce. It's nowhere near the expected investment needed to transition to a low-carbon future. And it's also nowhere near the loss and damage that many climate-vulnerable states are already experiencing every year,” said Gallogly-Swan.

“This isn't a question of rich countries' generosity,” she added. “This is a fair accounting of the differentiated responsibility that different states must bear for responding to climate change.”

A spokesperson from the Foreign, Commonwealth and Development Office said, “The UK remains unwaveringly committed to doubling our international climate finance to £11.6bn over the next five years.

“While the seismic impact of the pandemic on the UK economy has forced us to take tough but necessary decisions, the UK aid budget this year will still be more than £10bn.”