Final answer:
The question regarding the leader of the British Parliament from May until December 1848 cannot be answered because the provided information does not specify who held the position during that time, and therefore the success of said leader cannot be determined.
Step-by-step explanation:
The question regarding the leader of the Parliament from May until December 1848 cannot be answered directly as the provided information does not pertain to a specific individual who led the Parliament during that time. Instead, the provided information covers aspects of British parliamentary history and constitutional matters such as the Triennial Act, which required Parliament to meet every three years even if not called by the Crown, and the rule that no Catholic could become an English monarch.
In the 19th century, Britain's political arena saw leaders like Queen Victoria advocating for social justice, while notable politicians like Benjamin Disraeli and William Gladstone played pivotal roles in shaping the Conservative and Liberal Parties, respectively. However, without specific names or events connected to the period from May until December 1848, the success of the Parliament's leader during that timeframe cannot be determined.
Understanding that British politics was a complex mix of monarchy, Parliament, and evolving political parties can help provide context, even though the direct question cannot be answered with the given information.