1215. The TARDIS, as you might've already known from your own memories, travels through time as well as space.
In 1215, King John was on the throne in the absense of his brother King Richard I--Cœur de Lion, or "the Lionheart"--who was away to war, fighting in the Middle East--a place called... Jerusalem, I think? The Crusades, they were called--well, one of them. There were a lot fought, mostly over Jerusalem, a small, ancient city... the site claimed by many religions to be the Holy Land.
So a lot of people didn't really like King John. Men away to war, financial disaster to support the war which meant taxing the people more to sustain not just the war but the kingdom itself. Later, people will have it in history as him being a tyrannical king. A good bit of mythology as came out of the half-truths. Inventive stories, I should think.