Founded in 1991 as the WWF 1995 Group, the FTN aims to ensure members' timber and paper supplies come from well-managed forests and that products can be traced back to their source.
Robert Horne environmental manager Tim Barker said the firm's membership showed its commitment to the scheme and transparency.
"Customers can be reassured when they source from us that they are working with a company committed to environmental best practice," added Barker.
FTN manager Steve Crewe said Robert Horne's decision to join underlined its commitment to source materials from responsibly managed forests and recycled waste.
As a requirement of its membership, Robert Horne has published a responsible paper-purchasing policy and also adopted the Green Claims Code to ensure its communications are free of any vague or misleading environmental claims.
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