I am not a Roman Catholic but I am well aware of The Tablet as a weekly newspaper, & would expect any educated person capable of doing of a crossword of this standard to be aware of it too, along with the Church Times, Watchtower etc.
I'm not sure what else you needed, methyl? I typed Tablet into Google, & the first mention was a Jewish newspaper, & the second was 'British catholic weekly newspaper'. Surely that is enough to give you the correct context.