Once upon a time, in days of yore, in merry ole England soldiers in the King's service received a shilling as their wage. Interestingly the word shilling comes from schilling, an accounting term that dates back to Anglo-Saxon times when it was deemed to be the value of a cow in Kent or a sheep elsewhere. I remember as a child that my father kept some shillings as a souvenir but they had dropped out of circulation in England soon after I was born. In any event, the term 'to take the King's shilling' means to be in the employ of the Crown. The reason why I mention this is because I found out during my studies that if you wish to resign from Parliament this is exactly what one must do.
Apparently in 1624 a resolution was passed that election as a Member of Parliament is such a sacred trust that one can not resign their position. Obviously you can certainly lose your seat in an election, or you can die in office but what is one to do when there is a pressing need to leave the Commons for some reason. Recent events related to Parliament expenses has brought this to light - the MP must take the King's (or in this case the Queen's) shilling.
Based upon a provision in the Act of Settlement 1701, an MP who accepted a paid office under the Crown was obliged to leave the Commons and give up his position as an MP. The rationale being that his independence would be compromised if he were in the King's pay. As a result an MP who wished to give up his seat applied to the King for a post of the steward of an estate which had come into the ownership of the Crown. While such positions are archaic, really no more than in name only with little pay, they are taking the King's shilling nonetheless.
So now according to section 4 of the House of Commons Disqualification Act 1975 a member of the House of Commons becomes disqualified should they take the office of steward or bailiff of Her Majesty's three Chiltern Hundreds of Stoke, Desborough and Burnham, or of the Manor of Northstead. Still a rather spiffy title I should think.