John Major is threatening the next PM with a legal move to prevent Brexit.
In this situation of Britain leaving the E.U with the E.U not wanting to be left and actively intending to do anything it can [within the limits of its
own negative PR] Leaving with a deal is a non-starter. Therefore, John Major and all that are demanding a deal before leaving are simply attempting to prevent Brexit.
In the same way that John Major is going to use the courts to force the hand of the
PM and after Gina Miller did the same, it is about time that a PM used the courts to clarify [beyond the mendacity of political shenanigans] that Artical50 cannot be prevented by including an [undeliverable] condition or any condition [given that the extension
clause has already been exercised] and has amounted to no movement [or intention of movement] by the E.U.