SPHLC
Canberra Brake Control Valve - forward of the rudder pedals but under the cockpit floor, to give you yer differential braking.
Ah yes the Canberra BCV - in between the 2 floors - not so bad on a T4 because you could swing the nose open and actually see what you were doing LOL - but the Bomber variants were a pig !
ISTR that the aileron bias motor/spring were also 'down there' and also where you could touch it or feel it but not at the same time !