This is a hammered silver penny issued during the reign of Edward I (1272 - 1307).
King Edward I (also known as Edward Longshanks) was the first son of Henry III. Up until 1279, coins issued during his reign still featured the name of his father on them.
New coinage was introduced in 1279 and bore Edward's name. New denominations were also introduced, including the fourpenny (or groat).