Rishi Sunak is being urged to directly intervene to ensure Scotland's deposit return scheme (DRS) is not axed and can come into force next year as planned.

Groups such as Greenpeace UK, Keep Britain Tidy and the Marine Conservation Society have signed an open letter to the Prime Minister, demanding the UK Government grants an exemption for DRS in Scotland under the Internal Market Act - which regulates trade in the different parts of the UK following Brexit.

The exemption is needed as the scheme in Scotland is due to begin in March 2024, ahead of similar initiatives in England, Wales and Northern Ireland.

Scottish circular economy minister Lorna Slater has warned that if no exemption has been secured by the end of May, the scheme may not go ahead.

READ MORE: Deposit return scheme could be axed by end of May without exemption

With concerns that the UK Government will not have made a decision in that timeframe, charities and environmental organisations have called on Mr Sunak to act.

The letter, which has also been signed by the Association for the Protection of Rural Scotland, Friends of the Earth Scotland, WWF Scotland, Keep Scotland Beautiful, Keep Northern Ireland Beautiful and Keep Wales Tidy, also urges the PM to include glass bottles in the DRS schemes planned for England and Northern Ireland.

The DRS in Scotland was delayed after Humza Yousaf was installed as First Minister.

The scheme will see shoppers north of the border charged a 20p deposit every time they buy a drink in a can or a glass or plastic bottle, with that cash given back to them when the empty containers are returned for recycling.

It had been due to come into force in August, but its launch date has now been pushed back to March 2024 amid concerns from businesses about the impact it could have.

READ MORE: Lorna Slater unveils major changes to deposit return scheme

In their letter to the Prime Minister, the charities said DRS is "the single most effective policy tool available to reduce litter in our towns and countryside".

They told Mr Sunak that businesses in Scotland have "already invested hundreds of millions of pounds" ahead of the scheme being brought in, and they "would be substantially out of pocket if the launch date was changed again".

The letter continued: "The rollout of deposit return in Scotland in March 2024 will require an Internal Market Act exemption which we know is under discussion across Whitehall.

"Such an exemption will protect the substantial investment industry has already made in Scotland and ensure we start to see the environmental benefits as soon as possible."

The groups said Scotland launching a DRS first could be "actively beneficial for England, Wales and Northern Ireland", where the initiative is not due to come in until 2025.

READ MORE: Lorna Slater blames UK ministers for deposit return scheme delay

But they added: "There remains one key obstacle to a truly UK-wide approach to the litter problem. While Wales and Scotland intend to include glass drinks bottles, as things stand glass is excluded for England and Northern Ireland.

"If this remains the case, it would either undermine the long-term interoperability of the various systems, or cost English businesses more, unnecessarily, when glass is subsequently brought in, as happened in Finland in 2011 and elsewhere.

"We would therefore urge you to intervene and bring forward a straightforward solution to this problem by including glass on the same basis as Scotland and Wales, alongside the Internal Market Act exemption for the Scottish system."

The letter comes after Ms Slater said securing an exemption from the Internal Market Act by the end of this month is "absolutely essential to the successful delivery of the scheme".

The Scottish Green MSP said: "We have engaged with the UK Government in good faith on the exclusion for Scotland's deposit return scheme for nearly two years now.

"Despite following the mutually agreed process, we have still to be given necessary assurances that this will be provided in good time.

"This is creating uncertainty and confusion for all the businesses that have worked so hard to prepare for the scheme going live.

"I urge the UK Government to agree the exclusion by the end of May at the latest.

"Doing so is absolutely essential to the successful delivery of the scheme."

However Scottish Conservative Maurice Golden dismissed Ms Slater's claims as a "red herring", saying if the scheme fails it will be the Scottish Government's fault.

He insisted the financial viability of the scheme "is not encroached upon by an exemption from the Internal Market Act", as he accused Ms Slater and the Scottish Government of "attempting to stoke constitutional grievance" with Westminster.

Pressed on why the UK Government has not yet agreed to the exemption, Mr Golden told BBC Radio Scotland that there are not yet enough details available.

He said: "It's reasonable that we want to know what the scheme is before anyone can make a decision over whether an exemption could be granted."

A UK Government spokeswoman said: "UK Government ministers received a formal request for a UKIM Act exclusion for the Scottish Government’s Deposit Return Scheme on March 6 2023.

“The Scottish Government has since been reviewing and paused the scheme until March 2024 to allow it more time to address concerns raised by businesses. It therefore hasn't been possible yet for us to fully assess the impacts of the exclusion request on cross-UK trade, firms and consumers.

“We will continue to engage with the Scottish Government to realise our shared ambition to improve the environment while meeting the needs of consumers and businesses across the UK.”