DECC is currently consulting on Feed-in Tariffs for new biogas digesters: http://www.biofuelwatch.org.uk/2016/biogas-alert/. Turning some types of waste (e.g. sewage or food waste that couldn't be composted) into biogas makes sense, but the majority of biogas in the UK is made not from waste but from maize. Turning maize into biogas displaces food and animal feed production, and incentivises soil erosion, soil carbon losses, water pollution, and more severe flooding.
20% of all maize in England is currently grown for biogas. On top of this, the National Farmers Union has been calling for a major increase in the area of land used for this purpose.
Soil degradation is a major threat to our environment, to the climate, and to the future of farming. As a recent report by the Environmental Audit Committee points out, soils worldwide store three times as much carbon as is currently in the atmosphere. But soil carbon is being lost at a worrying rate in the UK.
Soil compaction and erosion are major contributors to flooding. Leaching of fertilisers and herbicides from eroding soils pollutes rivers and lakes. And of course, healthy crops depend on healthy soils.
Growing maize for biogas attracts double subsidies: Firstly, farmers are paid for growing maize and secondly, energy from biogas attracts renewable electricity subsidies and possibly also Renewable Heat Incentive payments. The Soil Association estimates that biogas subsidies for maize amount to around £50 million every year (in addition to the direct payments to farmers).