/u/telkanuru provides an excellent answer from the historical point of view. To this I would add Keith Thomas, Religion and the Decline of Magic (1971); although Thomas is discussing England of the sixteenth and seventeenth centuries, the magic - and world view - he is discussing is medieval.

From a folklore point of view, I will add a few things. The pre-industrial peasant - whether of the nineteenth or thirteenth century - changed little in his world view. If we find a peasant in 1830 who believes in magic or witches, we can surmise that we are seeing a worldview that is not unlike that of his counterpart, in the same village at least, in the medieval period.

With that in mind, folklorists find that beliefs can vary widely from person to person and from time to time. There have always been skeptics, and even believers go through skeptical moments. So there is really no universal. And what applies to people of a single place at a single time is magnified when one travels, so summing up a place as diverse as Britain during a time as diverse as the medieval period presents its own problems.

But what we find in work with pre-industrial peasants is an active belief system in witchcraft and demons and what you call "superstitions." I am currently working with material from Cornwall. The collectors Bottrell and Hunt worked with Cornish informants from the 1830s to the 1870s. They reveal a world view with active belief in witches, magic, and the sort of superstitions that you are asking about. After all the turmoil, from Protestant Reformation to a Puritan Parliament, here are these people in the west of Britain seeing the world in a way that one would expect of their medieval counterparts. They had active, sincere beliefs and they would probably have been shocked to find that anyone would be incredulous that they thought the way they did. That sort of evidence - which is widespread wherever folklorists worked with pre-industrial rural people in Britain suggests that the belief system you are asking about was prevalent and persistent.

One additional note: folklorists avoid terms like "superstitious" because they implies that "they" have silly beliefs unlike those of "my" culture. Every culture has some beliefs in luck or the supernatural. Folklorists avoid pejorative terms like "superstition." No big deal; just worth a mention.

Did your average layman actually believe that demons and witches were the heart of various problem, or was this a social construct to act as a scapegoat for the lack of knowledge as to why crops failed, people got sick etc.

There doesn't seem to be any meta thinking about it, if that's what you mean. This is stuff that people - common or not - honestly believed in.

Additionally, how devout was the average layman.

The average layman after 1215 would be expected to attend church yearly and tithe. He would also be very invested in his church as a sign of local pride.

how faithfully did people follow strict religious tenants

This is always a question which can't firmly be answered. "More or less" is about as much as I'd be willing to say.

Was there a genuine fear of hell?

You know the stock phrase "sure as hell"? As in "I sure as hell don't want to do that"? When people came up with it, you can be confident they thought hell was for sure.

I highly suggest you pick up a copy of:

• French, Katherine L. The People of the Parish: Community Life in a Late Medieval English Diocese. The Middle Ages Series. Philadelphia: University of Pennsylvania Press, 2001.

• Kieckhefer, Richard. European Witch Trials: Their Foundations in Popular and Learned Culture, 1300-1500. Berkeley: University of California Press, 1976.