Click painting to enlarge.
Easter Sunday 2013 will be 31 March.
Not coincidentally, the first night of the Jewish feast of Passover / Pesach will be Tuesday 26 March. Not coincidentally, because The Last Supper was a Passover supper. In the millennia since Jesus lived and died, there have been changes and reforms made to the Western Christian calendar, but the (incredibly complicated) algorithm for determining the date of Easter remains linked to the Passover -- they drift a few days from year to year, but Easter and Passover are always close.
As always, Stanley Spencer envisioned the events of the last days of Jesus' life using the familiar faces and feet of his neighbors in his village of Cookham, on the River Thames in England.
Jesus and the Apostles held their Passover supper in "the upper room," a private dining chamber above a tavern. Passover -- some say it's the world's oldest continuously celebrated religious festival -- celebrates the Jews' escape -- as the Greeks would say, the Exodus, the Going Out -- from Pharaoh's slavery and oppression in Egypt. Then and today, the Hebrew for Egypt is Mizrayim / מִצְרַיִם