The issue here is incredibly simple: predictablity.
The whole point of renewable energy sources is that we want to use them instead of conventional power generation. So the ideal situation is that we want to get the power from a renewable source and while we're getting that, we want to scale down the power we get from conventional energy and when the renewable stops providing, we want to scale the conventional energy back up.
Now, if you look at turbines, the picture is terrible. The wind is incredibly capricious and turbines can only operate at best 30% of the time. But which 30% of the time is completely impossible to tell.
The same applies, to a lesser extent, to solar power. Clouds may or may not have an effect on the capability of the panels, a snow dump could close them off for an unspecified period and if you place them in areas that have good weather and are more reliable, you generally lose a massive amount of power transmitting it to places that it's needed, completely subverting the value of the energy generated.
Even wave power can be significantly affected by the weather and time of the month. Although it will almost always be generating some power, it will almost never be consistent.
So why is this a problem? Well, with current power stations it can take hours or even days to adjust the amount of energy that is being produced.
If the wind is blowing sweetly, waves are nice and even and the sun is shining and we're getting a massive spike of "free" energy, by the time we've slowed down our existing coal and gas and nuclear power supplies, the situation will have changed completely and there will be blackouts all over the country. There would be chaos everywhere, every day.
People are working on this, but even if we were to decomission all our existing power stations and replace them with these which would require more than 200 of these power stations to be built (at a non-trivial cost) plus the cost of decomissioning existing power stations, all of this would probably bankrupt the UK.
And let's assume we beat Denmark's generation of renewable power and get to 30% of power being generated renewably. Given that a reasonable estimate of Britain's energy capacity at the moment is about 100GW, that means that 30GW could be provided renewably at any one time. This means that even using the latest whizz-bang technology, and assuming a completely even distribution of renewable power, there could, at any moment, be a 6-minute period where the entire country shuts down.
In practice, it simply means that we would either have to still massively over-provide electricity capacity, and that areas which have more access to renewable energy would be much more likely to experience an outage.
It doesn't matter how much power wind farms et al generate: if they can't generate the capacity predictably, then even while we're getting that power, we can't reduce the amount of conventional capacity we generate, so we can't reduce our horrid "carbon footprint" no matter how many cunting turbines we ruin the cuntryside with.
Update: This may have potential. (OK, that was pretty shocking. I'm sorry I didn't offer more resistance. Etc.)