A dual feedback control system was successfully implemented on JET to control high performing Ar seeded ELMy H-mode discharges. Controlled parameters are the confinement enhancement factor H98(y,2) and the total (or partial) radiated power fraction g = Prad/Ptot. Control parameters are the Deuterium and impurity (Ar) fuelling rates. This scheme was applied to trace T discharges and lead to discharges exhibiting the following performance: H98(y,2) 1, n/nGW 1, bn 2 and g = 0.65. The total radiated power was not significantly increased as compared to the unseeded reference case due to large intrinsic radiation inherent to the used configuration (HT3 with the MkIIGB-SRP divertor) and the "exchange" between intrinsic and extrinsic radiation. The time of penetration of T is higher in the Ar seeded case but this is essentially explained by the higher density reached.