The UK had a very effective efficiency program that they changed last year. At the time of the change government analysts stated unequivocally that the program as designed would be a complete failure. The response of the nucleo-maniacal Conservative government, of course, was to lick their chops and press on with great gusto.
From a Citigroup analysis of investment in new nuclear plants in Europe (with a focus on UK).
...Should EU countries go half way towards meeting their renewables target of 20% by 2020 that would be an extra ca. 440TWh. Even if EU went only half way, which by all means is a very conservative estimate, that would still be ca.220TWh of additional generation. Under its conservative scenario A forecast, UCTE expects 28GW of net new fossil fuel capacity to be constructed by 2020. On an average load factor of 45% for those plants thats an extra 110TWh.
Therefore under very conservative assumptions on renewables, we can reliably expect an extra 330TWh of electricity to be generated by 2020, leaving a shortfall of 16TWh to be made up by either energy efficiency or new nuclear.
There are currently 10GW of nuclear capacity under construction/development, including the UK proposed plants that should be on operation by 2020. If we assume that energy efficiency will not contribute, that would imply a load factor for the plants of 18%. Looking at the entire available nuclear fleet that would imply a load factor of just 76%. We do believe though that steps towards energy efficiency will also be taken, thus the impact on load factors could be larger.
Under a scenario of the renewables target being fully delivered then the load factor for nuclear would fall to 56%.