There is no one correct answer to this problem.
As a world we need to move to more local generation of power, this avoids the losses through transmission, its why the grid starts off at 400kv and reduces down as it gets to your house. The bigger the voltage the more efficient it is to transmit.
Yes new builds should be built to use the best of current technology, without needing to be subsidised. What to do with all the older buildings, millions of homes and commercial buildings to be torn down and rebuilt? My own house is listed and i'm prohibited from energy improving features becausce it would change the look of the house.. Madness.
Why build a barage across the Severn? That would be enviromental destruction on an enormous scale, millions of birds over winter there.
I'm not against Nuclear, but can't see how the business model works, 35 year payback on the new plant at Hinckley, but can't see another clean way to provide the base load on the grid. It would take an awful lot of undersea tidal generators to to provide that sort of power. But they have a place, a prototype has recently been commissioned off the coast of Pembrokeshire. Remember though that some industrial sites will use as much in services as a city, its not just a question of keeping the lights on.
Locally we have two pumped storage hydro-electric power stations that act like "batteries" fir the grid, there are others in Scotland. Another is planned a few miles away. More could be built, but unless you have a moutain range to loose them in.... not much use in southern England.
A lot of scare mongering is being used regarding fracking. The boreholes will be in to layers a long way below the aquifers, geologically different rocks, which is why thet contain gas or oil. Earthquakes, well coal mining and quarrying can produce them as well. It will happen because it move reliance away from foreign fuel sources, and because Joe Public like the easiness that comes with burning it.
I'm not an expert by any means, I'm not a left wing hippie, but I do think more can be done in a sustainable way, which requires a political will to liberalise planning laws and to modify building regs to allow greater use of local materials.
Just my two pennies worth....