I get that it stems from King Richard the lionheart. But this was 12th century England, and our most aggressive native animal is a badger. How were lions introduced to the English population at he time?
Some species of Lion did actually used to be native to Western Europe - but this is ancient history compared to the period you're talking about.
Knowledge about the Lion comes most likely from two main places:
The Romans imported Lions from their conquests in North Africa, to be used as entertainment across their Empire. The Bestiarii - a type of Gladiator who fought exotic animals like tigers, leapords, and Lions, became very well known. Now it's entirely possible that Lions were actually taken to Britain by the Romans - that i'm not sure - but they certainly took them to Italy, France and Iberia, so stories of them spread.
The Bible references the Lion 63 times. In this highly religious time, the educated and powerful would have known about them from their bible reading.
As /u/hdah24 points out, the lion was well known by people throughout Western Europe. When they were depicted as prowling and facing outward (like here) people referred to them as leopards. The first English king to adopt the lion as a personal symbol was Henry I (reigning from 1100-1135). He had a lion in his royal menagerie at Woodstock, which is likely the first lion most people in England would have seen in person. So even though lions were rare, they did exist in England at the time. Claims that Norman kings used the lion as a symbol were manufactured by later English kings; the Norman kings probably used a dragon.
Source: Stephen Friar and John Ferguson, Basic Heraldry, 1993.
