A more thorough explanation:

The Grenville Act was a law passed in 1770 that changed the way parliamentary election petitions were handled. Before the Grenville Act, the whole House of Commons would hear and decide on election petitions. However, the Grenville Act transferred this responsibility to select committees.

For example, if there was a dispute over the results of a parliamentary election, a select committee would be formed to investigate and make a decision. This allowed for a more focused and efficient process, as the select committee could devote all of their attention to the specific case at hand.

The Grenville Act remained in effect for almost 60 years, until it was repealed in 1828.