First Statute of Westminster
The word Parliament comes from the French word parlement. Parlement is derived from parler, to speak, and ment, which according to Bullet's Celtic dictionary, published in 1754, is synonymous with quantité. So Parliament means, lots of talk, a discussion. Some suggest a more ironic derivation for the word, that ment is derived from the French verb mentir, to lie. The first known use of the word mentir is the 10th century, well before the first Parliament, so maybe ... The second explanation certainly seems more appropriate in modern Britain.
The first English Parliament took place in 1265, during the reign of Henry III. The Parliament was called by Simon de Montford, who had captured Henry during the Barons Wars. Montford's Parliament was the first council to include elected representatives from the shires and boroughs - one of many reforms Montford's rebellion was about.
Montford died defending his reforms, but in 1275, Robert Burnell incorporated them into the first Statute of Westminster, passed during the reign of Edward I. According to William Stubbs, the British constitutional historian,
This act is almost a code by itself; it contains fifty-one clauses, and covers the whole ground of legislation. Its language now recalls that of Canute or Alfred, now anticipates that of our own day; on the one hand common right is to be done to all, as well poor as rich, without respect of persons; on the other, elections are to be free, and no man is by force, malice or menace, to disturb them. The spirit of the Great Charter is not less discernible: excessive amercements, abuses of wardship, irregular demands for feudal aids, are forbidden in the same words or by amending enactments.
Clause 15, known as the Freedom of Election Act 1275, is still in force today.