Impositions were introduced purposely and formally in the reign of James I. Impositions were a new source of royal income and were introduced in an effort to keep up with royal expenditure and also in an effort to reduce royal debt – both seemingly very difficult tasks for the likes of Robert Cecil and Lionel Cranfield, Lord Treasurer from 1621 to 1624. Impositions were duties on trade, additional to Customs duties, and were granted to James for life by his first Parliament.
Impositions had existed in the time of Mary Tudor and Elizabeth. However, they were on a small-scale and their legality had never been fully established. Parliament had never sanctioned impositions.
In 1606 impositions received a full legal standing from the Court of Exchequer which stated in its judgment that all imports and exports had to go through a royal port and that “they (the ports) are the gates of the king, and he hath absolute power by them to include or exclude whom he shall please.”