Derek Moran
12. No `scutage' or `aid' may be levied in our kingdom without its general consent, unless it is for the ransom of our person, to make our eldest son a knight, and (once) to marry our eldest daughter. For these purposes ouly a reasonable `aid' may be levied. `Aids' from the city of London are to be treated similarly.
http://www.britannia.com/history/docs/magna2.html