According to the wiki on Pumped-storage hydroelectricity (PSH), 'PSH accounts for more than 99% of bulk storage capacity worldwide: around 127,000MW, according to the Electric Power Research Institute (EPRI), the research arm of America's power utilities.' Since in pumping the size of the reservoir is not the limiting factor, but rather the throughput of the pumps, this means that PSH can be used to store the daily output of 127GW worth of power plants. Britain's consumption is 35.8GW on average, and 57.490GW at peak (http://en.wikipedia.org/wiki/Energy_in_the_United_Kingdom), so the global installed PSH's could easily absorb the UK's production.
In the UK, however, there seems to be only one plant (http://en.wikipedia.org/wiki/Dinorwig_Power_Station), costing 425M GBP in 1974 capable of absorbing around 1GW worth of power, so nowhere near 50% of base load, so it seems that PSH costs around 425M/1G = 0.5 pounds per watt capacity. Apparently, a new nuclear plant costs about US$ 5,339/kW., or 4 pounds per watt capacity, while windmills cost around 1-2 pounds per watt. So, assuming enough sites for PSH can be found, the costs for power storage capacity seems to be 5-25% of the cost for generation capacity.
According to the wiki, "The stalling of the UK nuclear power programme in the late 1980s and the coincident "dash for gas" increased the network's ability to respond to changes in demand, making the use of pumped storage for day/night load balancing less attractive. As a result, a similar facility planned for Exmoor was never built.[2]"; so it seems that at the time the demand is what limited PSH construction, not cost or environmental factors.
http://www.world-nuclear.org/i...
http://www.windustry.org/resou...