A Green Card is a card that you fill in if you want to see your MP at the Palace of Westminster. If you want to visit your MP at the House of Commons you can go through the public entrance of the building and fill out your details on a Green Card in the Central Lobby. The officials in the building will then make every possible attempt to find the MP and ask him or her to meet you in the Central Lobby. If the MP cannot be found a message is left. MPs are not always in Westminster as they have a lot of work to do in their constituencies and elsewhere and it is best to make an appointment in advance.