National Highways and environmental sustainability

Status / emerging findings

• Only 53% of ecological mitigation commitments are delivered; 73% of failures involve missing woodland planting. The A14 scheme saw 45% tree mortality (160,000 trees) due to basic execution failures like poor timing, inadequate watering, and wrong species for exposed sites.
• Highway pollution is almost entirely unregulated: the Environment Agency has issued zero permits for highway discharge despite statutory responsibility. Every water sample from National Highways schemes fails environmental quality standards for hydrocarbons.
• Of 25,000 highway outfalls, only 126 are targeted for treatment by 2030. Existing mitigation designs are undersized: M6 vortex separators remove only 40% of suspended solids versus required standards.
• Local planning authorities lack ecological expertise (only one-third have in-house skills) to monitor compliance. National Highways' post-operational monitoring is severely deficient: only 1 of 20 projects reviewed showed adequate oversight.
• Replanting trials using proper horticultural practice (plug plants, mulch, watering) achieved under 15% dieback, proving the original A14 failures were preventable with standard knowledge.

Why it matters

National Highways controls one of the UK's largest infrastructure portfolios; systemic failures in tree planting and pollution control undermine climate adaptation, biodiversity targets, and water quality across England—yet regulatory oversight is nearly absent.

Tone arc

Opened procedurally but turned sharply adversarial after expert witnesses (Woodland Trust, Kew Gardens, Environment Agency) revealed systematic failures. National Highways' CEO conceded basic horticultural mistakes and regulatory gaps, shifting from defensive to commitments to improve.

Key witnesses

Nicole Hillier (Woodland Trust), Kevin Martin (Royal Botanic Gardens, Kew), Jo Bradley (Stormwater Shepherds, formerly Environment Agency), Catherine Moncrieff (Chartered Institution of Water and Environmental Management), Nick Harris (National Highways Chief Executive), Stephen Elderkin (National Highways Director of Environmental Sustainability)