Legend suggests that Joseph of Arimathea, was the Lord's uncle (maternal no doubt), that he owned tin mines in Cornwall (England), and that Jesus may have accompanied him in a trip to Britain as a youngster. From that the legend grew.
Blake of course was familiar with both stories (the biblical one and the legendary one), and they led to the famous poem and hymn called Jerusalem that appears in the Preface of Milton. Here are the tune and words:
And did those feet in ancient time,
Walk upon Englands mountains green:
And was the holy Lamb of God,
On Englands pleasant pastures seen!
And did the Countenance Divine,
Shine forth upon our clouded hills?
And was Jerusalem builded here,
Among these dark Satanic Mills?
Bring me my Bow of burning gold:
Bring me my Arrows of desire:
Bring me my Spear: O clouds unfold!
Bring me my Chariot of fire!
I will not cease from Mental Fight,
Nor shall my sword sleep in my hand:
Till we have built Jerusalem,
In Englands green & pleasant Land.
(Would to God that all the Lords people were Prophets.) Numbers XI. ch 29 v.
This hymn became immensely popular and bid fair
to replace God Save the King (at least in some circles.)