 The P.120 followed the earlier Boulton Paul P.111 delta-wing experimental aircraft.It was produced for the Air Ministry to specification E.27/49 and differed from the P.111 in having a swept fin and rudder with horizontal tail surfaces high on the fin to improve longitudinal and directional stability.It had essentially the same wing as the P.111 in the latter's greatest span configuration, an unclipped delta; the wing tips of the P.120 were not removable or replaceable, but they could be rotated differentially or together for lateral or longitudinal trim.