The monarchy came closest to being absolute during the Tudor period and the early Stuarts. Charles I managed to rule without Parliament for a while. He was forced to call Parliament in 1640 to deal with a revolt in Scotland. I believe the reason he couldn't do it by fiat was the Magna Carta. Thus came the Short Parliament, which proved too rebellious for his taste, then the Long Parliament, which challenged him by the British Civil War. There are parallels with the later French Revolution, complete with the beheading of the King and the eventual rise of a military dictator. In 1660, when Cromwell's successor proved unable to rule, the English brought back Charles's son, Charles II, with the understanding that he would regularly summon Parliament. In 1688, the Bill of Rights considerably strengthened Parliament, and that's really when England became a constitutional monarchy, although some of the monarchs, such as George III, had considerable power. George III, for example, selected Lord North and William Pitt the Younger to be Prime Minister. More recently, Elizabeth II in 1963 selected the Earl of Home to be Prime Minister after Harold Macmillan was diagnosed with prostate cancer (although she consulted with Conservative leaders before doing so).