The claim is widely discredited among historians, because the evidence for Sol Invictus being celebrated on December 25 appears later than the first records of Christians saying Christ was born on the date. Chris McBride, a historical researcher, responded to the post: “You are one of the highest, most important historical bodies in the country. Guardians of historical knowledge. How can you still not know this is utter nonsense? This has nothing to do with why Christmas is on December 25th.”

The charity, which later admitted it got the facts “wrong”, was also criticised in April after one of its sites claimed Easter was not originally Christian. Dr Bijan Omrani, the historian and author of God is an Englishman, told The Telegraph: “Earlier this year, English Heritage relied on outdated or discredited scholarship to argue that Easter was developed out of pagan festivals. It is unfortunate that they have done the same again about Christmas."