From the BBC New UK high-speed rail plan unveiled
The line would serve Birmingham and Manchester, getting passengers from Glasgow to London in just two hours and 16 minutes, the rail firm said. It rejected several alternative routes, including the east of England.
Judging from the map (linked below), the architecture of the line is clearly to feed London, all of the ancillary cities are as if on a tree with the xylem and phloem oriented to London, it would not be terribly good for say Manchester to Edinburgh or Manchester to Birmingham.
"The firm said that the line would account for 43.7 million journeys per year by 2030, which would result in 3.8 million fewer vehicle journeys and fewer carbon dioxide emissions.".In other words, more 90% of the trips are switching from rail or air to HSR. Providing better rail service to existing rail passengers is a good thing, but CO2 is hardly a rationale (as more CO2 has to be used going faster than going slower if the electricity is from the same place ... diesel to electric conversion is a separate matter).
Finally, the cost is esimated at $55B for 1500 miles of rail (presumably including triple or quadruple tracking in some sections. Planning will take 5 more years. It is hoped by the promoters the first section (London to Birmingham) will open in 2020. Speeds will max at 200 mph.
Also see: London to Glasgow in five minutes, a video showing the West Coast Main Line (which this proposal seems to duplicate) and was recently modernized for 9 billion pounds.