In a way, this research is pointless because I'm 100% sure that Keith Windham is not interested in being a Dissenter--he seems to be a default Anglican who is not interested in religion. But I had written a line in a fic where the question arises (though it was not actually necessary for the plot). Then
garonne noted that Keith could only really be an Anglican because that was required of all state officials, including military officers (or, well, they had to take Anglican communion once a year, at least). But I suspected that this would not be true because Keith is in a Scottish regiment.
It was surprisingly difficult to find information on this online, though now I see that if I had only used the right search terms, I would have found it--but of course the right search terms were part of what I didn't know. But finally in the article 'The Realities of Toleration: Army Chaplaincy, Religious Politics and Scottish military experience, c. 1690 to 1763', by Xiang Wei (2023), I found the answer. I could not get hold of it online by myself, and I bless the university library for never asking why someone in the math department would want to read such an article (is this in fact part of their professional code?).
So in the 17th century Restoration, Anglicanism/Episcopalianism was imposed on the whole of Britain, and required of all state officials. Then in the Glorious Revolution the Presbyterian Kirk gained ascendancy in Scotland, so that all officials had to be Presbyterian there. But in 1712, the Toleration Act changed this (but only in Scotland!), so that it was okay for government officials to be either Presbyterian, Episcopalian, or Anglican (and perhaps further Protestant denominations, I don't know how far it stretched). Not only that, the Patronage Act also opened the door for army chaplains not to be Presbyterian (because lay patrons could appoint ministers and they didn't have to appointed by the local congregations, which the Presbyterian Kirk wanted). Of course, there was controversy about this, with the Kirk wanting to gain control over the appointment of army chaplains--but over the course of the 18th century, the army increasingly controlled such appointments. Scotland having toleration but Ireland and England not having it caused some problems when regiments moved across borders. For example, there was an incident where a Presbyterian army chaplain was fired when his regiment was deployed to Ireland. He tried to fight this legally, but lost.
Anyway, there you go, I was right! Keith could have been Presbyterian, or probably some sort of Dissenter, if he had wanted to. Some of his colleagues probably are.
It was surprisingly difficult to find information on this online, though now I see that if I had only used the right search terms, I would have found it--but of course the right search terms were part of what I didn't know. But finally in the article 'The Realities of Toleration: Army Chaplaincy, Religious Politics and Scottish military experience, c. 1690 to 1763', by Xiang Wei (2023), I found the answer. I could not get hold of it online by myself, and I bless the university library for never asking why someone in the math department would want to read such an article (is this in fact part of their professional code?).
So in the 17th century Restoration, Anglicanism/Episcopalianism was imposed on the whole of Britain, and required of all state officials. Then in the Glorious Revolution the Presbyterian Kirk gained ascendancy in Scotland, so that all officials had to be Presbyterian there. But in 1712, the Toleration Act changed this (but only in Scotland!), so that it was okay for government officials to be either Presbyterian, Episcopalian, or Anglican (and perhaps further Protestant denominations, I don't know how far it stretched). Not only that, the Patronage Act also opened the door for army chaplains not to be Presbyterian (because lay patrons could appoint ministers and they didn't have to appointed by the local congregations, which the Presbyterian Kirk wanted). Of course, there was controversy about this, with the Kirk wanting to gain control over the appointment of army chaplains--but over the course of the 18th century, the army increasingly controlled such appointments. Scotland having toleration but Ireland and England not having it caused some problems when regiments moved across borders. For example, there was an incident where a Presbyterian army chaplain was fired when his regiment was deployed to Ireland. He tried to fight this legally, but lost.
Anyway, there you go, I was right! Keith could have been Presbyterian, or probably some sort of Dissenter, if he had wanted to. Some of his colleagues probably are.