The Government do not make separate estimates for future levels of generating capacity in different parts of Great Britain. Scenarios for future electricity generating capacity in the UK are set out in the Updated Energy Projections of February 2008, available at
http://www.berr.gov.uk/files/file39580.pdf.
These projections do not, however, take account of any policy changes that may be made in pursuance of the Renewables Energy Strategy, which will be published next spring.