[pixelesque]

Roughly that figure (45%) was used to get to Mach 2.0 at 60,000 feet, about 45 minutes after takeoff from LHR (normally over the Bristol channel) to JFK.

Takeoff and climb / accel to Mach 1.7 was done with re-heat (afterburners), which did use a lot of fuel. After that, normal power (no re-heat) was used to get to Mach 2.0 and cruising (supercruise).