Heraclios, not Heraclius. It's a Greek name. Heraclius is the Latinized version, and Latin was out of use in the Empire by his time. It was already sparsely used during the reign of Justinian I (527-565), who made quite an effort to hire someone who still spoke Latin, so all the old laws could be translated and compiled into Corpus Iuris Civilis (Body of Civil Law). Heraclios finally made Greek the official language of the Empire. His name was Ἡράκλειος', which is read as Iráklios.
The follis was minted since the reign of Diocletian, not only for its duration. Wikipedia says that it "was reintroduced as a large bronze coin in 498", so it was definitely still in use after 313, if Wikipedia is correct.
Also, there is no indication that this coin was minted after 313, because we don't know what the symbols are. @PRJKTLRD only assumed they could be Christian, but nothing is certain. If this is a follis, however, it is definitely younger than 294, because that's the year Wikipedia says the follis was introduced, if Wikipedia is correct.
We'll get a certain date when we can read the text on the coin's face, because it should say who the person printed on it is. My guess is either Valentinian I (364-375) or Theodosius I (379-395), by the look of the person.
It might not be as much of a sensation as it seems, though. Wikipedia says that the 4th century follis is the most frequently found ancient coin in Britain. I've done a search on eBay and the average sale price of a follis from the reign of Theodosius I is... 10 euros