As environment minister, he introduced the plastic bag tax which reduced the use of personal bags by 85% in 6 months; and he was responsible for producing the first draft of the 25-year environment plan in which he emphasised, alongside biodiversity and ecosystems, the importance of human cultural features in the landscape, and particularly the conservation of small family sheep farms. As Minister responsible for the National Parks, Stewart secured five years of increased funding for national parks and AONBs. He also ensured the extension of the Lake District and Yorkshire Dales National Park and supported the UNESCO World Heritage bid for the Lake District.