The report said a network of 200 mph-an-hour services could slash journey times between London, northern England, Scotland, Wales and the South-west, and regenerate communities on the routes.
Ministers were advised in the report that without dedicated, high-speed lines there would be major capacity constraints on intercity routes.
Commission chair David Begg said: "The year 2015 is a key juncture for us in terms of our capacity limit. But, given the long lead times, planning needs to start now."
The report warned that the cost of new infrastructure needed to be reduced. It said that building train lines in phases rather than all at once could produce cost savings of 20-30%, and a review of safety regulations could cut costs further.
The report said: "There is also scope for savings from project management, planning, design and legal costs, which can add up to 25% of total costs."