Diageo, Reckitt Benckiser and Unilever are the companies combining the best results in slashing greenhouse gas emissions with the most transparent reporting, according to a new study released this week.

The Carbon Disclosure Project names the suppliers as standing out among 238 companies it rated, scoring all with an A for performance.

Drinks giant Diageo led the field with a 98 score out of 100 on transparency, compared with RB with 93 and Unilever with 84.

Tesco scored 91 for transparency but a B for performance.

The CDP, a not-for-profit body that worked with leading accountants PwC on the report, claims the scores show how the most transparent companies can transform their performance in cutting emissions, with the government poised to make such reporting mandatory for listed companies from April next year.

“Companies are increasingly aware that they need to provide a complete story to all stakeholders and report on all factors that could affect their long-term prosperity”, says the report. “The process of reporting through CDP, as shown by the highest-scoring companies, brings about strategic change.”

RB said it was now aiming for “further dramatic progress on carbon” on the back of the results. Tesco climate change director Helen Fleming claimed the government’s move was a “critical step on the road to establishing a greener economy in the UK.”

But CDP questioned whether the plans went far enough for investors. “It does not currently specify a standardised reporting approach for compliance, failing to introduce reporting that will produce consistent and comparable information within a structure that could be adopted by other national jurisdictions,” it said. “Furthermore, it does not demand companies make a full assessment of how climate change is expected to affect their business. These points directly impact how much value investors will be able to derive from any mandatory reporting. Without this being addressed there is a risk that the regulation will not reach its full potential.”