Let's be absolutely clear. There is very little to object to about fracking. The issue is almost entirely political. Groundwater contamination can be avoided, and the threat of earthquakes is just grotesquely exaggerated. There are "seismic events" but they're equivalent to someone dropping a bowling ball out of a tree. Detectable, but unlikely to knock your house down. Any objections remaining are "general industrial" objections to plant and machinery moving about. But fracking plants aren't particularly big, or noisy and when plumbed into a grid, don't require much in the way of plant moving about.
The environmental benefits are mainly from replacing coal. Coal is dirty, and produces more particulates and sulphur (things that actually destroy lungs and trees) than gas. Per unit of energy, it also produces more carbon dioxide than gas at the power station. One of the objections to fracking is that leaks of Methane from the process enter the atmosphere. These leaks can almost entirely dispel any benefit to Greenhouse emissions as Methane is a far more potent Greenhouse gas than Carbon Dioxide. However CO2 accumulates in the Atmosphere, whereas methane breaks down quickly. EPA estimates of leaks range from 2% (at which level there are clear greenhouse benefits to Gas) to 14% (at one rig in Utah, which appeared to be an outlier).
Methane leakage is a regulatory and engineering problem. It isn't fundamental to the technology.
Cameron thinks Fracking can reduce energy bills. Well he's half right. If the technology is adopted across Europe, then yes, it will but UK supply will be fed into a European gas network, and will unlikely be enough to significantly alter prices on its own. What will happen is that taxes will be levied on production and the majority of the benefit will flow to the exchequer. Furthermore, the balance of trade will improve, probably strengthening Sterling as we once again become an energy exporter. This will help to reverse the slide in living standards as imports will become cheaper again.
No-doubt Labour, gifted Lord Howell's remarks about the "desolate" North East being suitable for Fracking, then rowing back by saying he meant the North-West (well that's OK then...) will make this about a posh, southern "them" doing fracking to the poor, benighted north. Hence Cameron pointing out that much of the shale is in the South East of England, and his (neighbouring) constituencies had better get used to it.
Fracking. It may make your Gas bill a bit lower, but the main effect will be on helping to close the fiscal gap, reducing the pressure on the rest of the economy, and generate cheap, relatively clean energy. The risks are grotesquely overstated by the sort of people who would object to anything, anywhere, ever.
The US Environmental Protection Agency is due to report in November. But they seem to be saying in their update report that most of the problems so far identified are exaggerated, and soluble. The potential benefits to the UK are far more than lower energy bills, and most of the objections are spurious. Let's just get on with it. Cameron's right. Let's frack, baby frack.