Not sure what exactly you're meaning with QED in this instance, but if you're saying that the AirTanker contract also precludes the BAE 146 being used then that's incorrect. The contract says the MoD cannot tank with anyone other than AirTanker, but does not say it cannot tank with any platform other than Voyager.
BAE thinks (rightly or wrongly) that there is scope in AirTanker operating a small number of 146s to augment the Voyagers for training and tactical tanking.