The Grey family finally captured the English throne at the second attempt but only because of the circumstances of the Cousin's War with Scotland.
12th February, 1568 - Elizabeth Tudor follows Cousin Mary in deathHenry VIII's death had caused a long-term succession crisis in the Tudor Court because of the sibling rivalries resulting from his polygamy and also the legitimacy laws that he had been changing around on several occasions. Indeed Elizabeth herself had become Queen largely because of her predecessor's unpopularity in the country rather than the letter of the law. Through various political devices to discourage Catholicism she was keen to speed-up the Protestantization that had begun under the regency of Edward VI. And so she was unnecessarily confronted by fierce resistance from Papists in many guises even though a counter-reformation was rather unlikely. This was primary because of the resistance from the new owners of the lands seized from the Church, "I'm not greedy for land. I just want what adjoins mine!" their battle cry.
However Elizabeth was unable to restore control over the State which the Tudors had themselves established. Her agents arranged for the murder of Mary Queen of Scots but this regicide only sparked a bloody act of revenge in which Elizabeth herself was murdered by Scottish agents. And so the succession would read Henry VIII - Edward VI - Lady Jane Grey - Mary Stuart - Elizabeth Tudor - Lady Catherine Grey. Inevitably despite (rather than because of) these rapid leadership changes and mainly due to the effective us of the printing press the Protestant reform had proceeded at a steady pace during this succession crisis. Perhaps if they'd been willing to accept the loss of lands, then the Catholic church could have recovered. But no matter because of Elizabeth's infertility the Tudors were busted anyway. And a usurpation by the Stuarts would perhaps only have re-opened a Papist struggle not to say create a personal union which in the long-term might well have destroyed the sovereignty of an independent Scotland.