memes

They also lost faith in Catholicism when the IRA failed to kill her.

Such a steep drop seemed suspicious, so I sought out the source of the graph.

Just skimming over the sources cited, while it's clear that you do see a larger decline for Anglican/Protestant than the other categories, I didn't notice anything quite so sharp. If you look at the description for the graph, the author explains that the decline is due to a change in survey method (emphasis mine):

The line denoted at 1980 shown is there to represent a shift in sources from Gallup opinion polls which were taken from 1947 to 1978 to BSA Faith in Britain surveys conducted which has a better survey question ("Do you regard yourself as belonging to any particular religion? IF YES: Which?"); primarily, the BSA source is superior due to the fact it filters out 'Christian nominals', those that are not necessarily religious (hence 'belong') but 'identify' with a specific [denomination] due to their cultural upbringing/background getting a more accurate figure of religious affiliation.

So basically, the sharp drop doesn't reflect an actual steep drop, but rather that religiosity was already lower than previously recorded if you use that stricter standard.

edit: "authors explain" → "author explains"

The average Briton had to contend with the question evil for the first time

Whoah the non-christian population is so much smaller than I thought. With all the South Asian heritage I thought there's be at least 10% other.