The "Non-Jurors" were those clerics and laics of the Church of England who, having sworn an oath of allegiance to (the still living) King James VII and II, refused to disregard it by swearing a new oath to the Calvinist intruder William Prince of Orange after he invaded this country in 1688. They were accordingly evicted from their livings but maintained that they remained the true, if persecuted, Church of England for much of the 18th century. Many of them were Jacobites.
Some of them stuck rigidly to the then current Book of Common Prayer; others, more Catholic minded, deemed themselves to have the right to catholicise (often from Eastern sources) their worship. These latter were known as the Usagers.The Usagers issued, in 1720 (NS), their own Prayer Book. Certain features of this (especially its Eucharistic Order) are known and publicly accessible; but I do not know that the whole book is. One copy I have examined is in the 'Sion College' Library, ARC A 35 1b N 73.
A problem arose, of course, with regard to the State Prayers, which could not be used as they stood by those who denied that "King George" was their true Sovereign.
Thus, after the end of the Divine Office, "A prayer for the King's Majesty" included the words " ... behold our most gracious Sovereign Lord King George ...". This, obviously, could not be used by those who regarded the exiled King James VIII and III as their lawful king.
They therefore, changed it to "behold our most gracious Sovereign Lord the King".
In "A prayer for the Royal Family", the Non-Jurors were able simply to delete the entire list of members of the Hannoverian family, and to pray " ... bless all the Royal Family ... ".
In the 19th and 20th centuries, things were made more complicated by the fact that the de facto sovereign (e.g. Victoria) was often of a different gender than the King Over The Water.
For the minute group who still preserved this ancient loyalty, the same problem remained because the King de jure (Francis of Bavaria, direct heir of the exiled Stuarts) was of the opposite gender from the Queen de facto, Elizabeth, direct descendant of George I of Hannover.
There was faintest, imperceptible, batsqueak echo of this old history last Thursday when Mgr Newton, before Evensong in Warwick Street, announced the news that Queen Elizabeth had died; and that therefore, the officiant would be singing O Lord, save the King.
(After James III and VIII died in 1766, his de jure successor was, of course, the de jure King Charles III, who 'reigned' until his death in 1788. I haven't seen this little historical whimsy mentioned in recent newspapers.)