Quoting Smilin Ed:
Again, apparently appropriate electrical signals reached the engines and individual parts of the engines responded accordingly but the engines just didn't produce the demanded power.
According to the AAIB report, engine fuel control systems functioned normally. However, if fuel flow (from airplane fuel system) to the engines is somehow restricted and cannot meet engine (control) demand, the engines will only accelerate to- and stabilize at the restricted fuel flow value, regardless of normally functioning fuel controls on the engines.
Green-dot