Congress and Parliament have many differences including the meaning of their names, Congress meaning "a coming together" and Parliament "to talk." Both consisting of members representing their local districts, the way in which these members are selected are far different from one another. In Britain, local committees of national political parties select the members of parliament and the voters choose between national parties. In the United States, a person would have to run in a primary to get on the election ballot and the voters choose based on more so on personality rather than political party. The actual political party has little to do with this process even though the candidates will describe themselves with a party label. Once in office a Member of Parliament is limited to voting to support or to not support the government. In a Parliamentary system the party that holds the most seats will choose a Prime Minister.
That party will remain in power as long as they follow their leader or until the next election. The U.S. Congress is separated from the executive branch and in turn do not select the President. Members of Congress fell less of an obligation to vote with their party than do members of Parliament because the political parties hold less power over their futures. While the principal work done in Parliament is debating, Congress represents the people and takes action.