A candidate for a seat must submit nomination papers signed by ten registered voters from that area, and pay £500, which is refunded if the candidate wins at least five per cent of the vote. Such a deposit seeks to discourage frivolity and very long ballot papers which would cause vote splitting (and arguably voter confusion). Each constituency is also called a seat (as it was in 1885), as it returns one member, using the first-past-the-post electoral system, under which the candidate with a plurality of votes wins, that is greatest number of votes. Minors (that is, anyone under the age of 18), members of the House of Lords, and prisoners are not qualified to become members of the House of Commons. To vote, one must be a UK resident and a British citizen, or a citizen of a British overseas territory, of the Republic of Ireland, or of a member of the Commonwealth of Nations. British citizens living abroad are allowed to vote for 15 years after leaving. It is a criminal offence for a person to vote in the ballot of more than one seat which is vacant at any election. This has not always been the case: before 1948 plural voting was permitted as voters qualified by home ownership or residence and could vote under both entitlements simultaneously, as well as for a university constituency if a university graduate.