Under current policies, renewables would need to grow from their current 5-6% to 30-40% to meet the 2020 targets. The higher costs associated with renewable generation, in comparison to conventional or nuclear, would raise electricity generation and transmission costs by £6.8 billion ($10.5 billion) per year, a 38% increase that would have to be met by UK consumers.
UK government report - entitled The Economics of Renewable Energy