In addition, the 2011 Act mandated a referendum in 2011 on changing from the current "first-past-the-post" system to an alternative vote (instant-runoff) system for elections to the Commons. The Conservative–Liberal Democrat coalition agreement committed the coalition government to such a referendum. The referendum was held in May 2011 and resulted in the retention of the existing voting system. Before the previous general election the Liberal Democrats had pledged to change the voting system, and the Labour Party pledged to have a referendum about any such change. The Conservatives, however, promised to keep the first-past-the-post system, but to reduce the number of constituencies by 10%. Liberal Democrat plans were to reduce the number of MPs to 500, and for them to be elected using a proportional system.