Tornado is only faster than Buccaneer at low level when completely clean, ie useless, as it carries everything externally. The Buccaneer has a better transonic drag profile than the Tornado so although the overall top speed is much lower, the transonic drag rise at low level is far less severe with the Buccaneer, the Buccaneer was faster with four sea Eagles under the wings at low level than the Tornado is when carrying two of them plus two hindenburgers (which is its max and another advantage of the Bucc)
The buccaneer could carry a 4,000lb load internally and bomb a target for which the Tornado would have to carry the four bombs under the fuselage and, again, two hindenburgers on the inner pylons to match the range and would cruise about 100kt slower.