In September 2006, Walker joined other leading UK publishers to set up the Publishers' Database for Responsible Environmental Paper Sourcing (PREPS), with the aim of ensuring that we all use legally harvested and sustainable forest sources. PREPS hold technical specifications and details of the pulps and forest sources for each of the papers used by its members. Based on that information, papers are awarded a grade of between one and five stars using the Egmont Grading System, which evaluates whether material has been legally harvested – or recycled – and how the forest sources have been managed. It encompasses FSC and PEFC certification.