It was not the first time that a Convention Parliament had effectively determined the succession. We might look, for example, the precedent of 1399, when just such an assembly deposed Richard II and (in effect) elected Henry IV, who was not even Richard II’s right heir. (He was the heir male, but strangely enough did not claim on that basis.) Of course, in 1399 Henry’s very large army was in place in the London area, and it would have been difficult for the Parliament to have rejected him, even had it wished to do so.
Richard, Duke of Gloucester, had no equivalent army in London when the Three Estates met. It is worth remembering that Parliament could reject claims to the throne it did not care to approve. The obvious example is that of Richard’s own father, Richard, Duke of York, who had his very strong claim rejected in 1460. Peers did not show up at Parliament unattended, and if they had strongly objected to Richard’s claim they could easily have mobilised their forces against him, if necessary. The fact is, they chose not to do so.
It seems certain that evidence of Edward IV’s bigamy was presented to the Estates. Sadly, we do not know the details and never will. But it is certain that among the bishops there were no shortage of theologians, any one of whom could have stood up and protested against the accession of Gloucester at very little personal risk to themselves. True, they might conceivably have been imprisoned, but what is that to a senior churchman when the immortal soul is at risk? In 1399, the Bishop of Carlisle objected openly to Richard II’s deposition, and was imprisoned for it, but he survived. There is no evidence of any bishop speaking up for Edward V.
Finally, it is sometimes argued that the legitimacy of Edward V was a matter that ought to have been determined by a Church court. However, the idea that the Parliament of England in the late fifteenth century would allow the succession to be determined by one or more bishops, or even by the Pope, is rather naive. It was, after all, only half a century later that Thomas More and Richard Rich agreed between themselves that Parliament had the power to make Richard Rich king, if it chose to do so.