What developments in medieval england influenced modern democratic law?

 In medieval times, the kings were limited by the manorial economy. For foreign wars, they needed to raise money that was unavailable outside of feudal customs. They needed special grants of money. 

Men in those days studied law, and one law that they studied was ancient Roman law. There was a principle of Roman law that, "What concerns all should be approved by all." 

The kings began to summon meetings of parliaments, consisting of the three estates of society: The clergy, the nobility, and the commons. At that time, the commons were delegates from independent cities and towns. The clerical and noble delegates met with the king in one chamber while the commons waited outside. A spokesman came to announce that the clergy and nobles had voted the money to the king and invited the commons to do so. 

After some years, the commons elected one of their number as their speaker. When the spokesman came to get their agreement, the speaker named certain changes that the commons wanted to see made first. Through the years, kings felt the need to summon parliaments more and more, and the commons were able to put forth more demands. 

Interestingly, the principle of Roman law that brought all this about was one governing business partnerships