It is difficult to accurately predict the amount of installed capacity for unabated coal and gas in 2025, as (provided they continue to comply with environmental legislation) the decision to retire old plants, and build new ones, is a commercial matter for individual plant operators.
The Carbon Plan, which was published on 1 December 2011, sets out a range of scenarios to highlight the possibilities and the challenges we will face in decarbonising the economy between now and 2050, using currently available knowledge. At this stage, it is not possible to predict with certainty the most cost-effective route to decarbonisation of the power sector and the scenarios are not intended to present a definitive assessment of a particular technology.
Some estimates of future installed capacity, and the assumptions underlying these estimates, can be found in the following:
DECC's Updated Emissions Projections
DECC's Carbon Plan