Communications firm BT has topped the rankings of Carbon Clear's assessment of FTSE 100 company's carbon reporting for the third year running.

The carbon advisory service's survey scores the companies based on their monitoring, reporting and verification; their carbon strategy; carbon reduction; stakeholder engagement and innovation. The retailer Marks and Spencer was ranked second again while food company, Unilever, moved up to third position.

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As well as scoring the companies Carbon Clear's report, examined best practice carbon reporting processes and procedures and changes in energy use. The survey found that 48 FTSE 100 companies purchase green electricity while 10 firms have committed themselves to RE100. This is a  collaborative, global initiative of influential businesses committed to 100% renewable electricity.

Additionally 66 companies show an assessment of materiality of climate change issues, or an assessment of the risks climate change poses to their business. The research has also found that six companies have now set science-based targets for reducing carbon emissions while six more are committed to doing this in the future. Reporting on indirect carbon emissions (known as scope 3 reporting) has also improved with 66 companies reporting on Scope 3 data, 10 more than 2015 with over 70% of these reporting beyond business travel alone.

Looking at specific sectors the survey found that supermarkets are the best performing sector with an average score of 59% although this is down from 74% last year. Meanwhile engineering and machinery are the worst performing sector with an average score of 26%, down from 34% in 2015.