Inspired by the imp who set loose a snake in the monastery? (4,6)

I believe the answer is:

holy terror

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'imp who set loose a snake in the monastery?' is the definition.
'holy terror' can be an answer for 'imp' (holy terror is a kind of imp). I am not sure about the remainder of the definition.

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for holy terror that I've seen before include "Very tiresome child" , "Troublesome child" , "One who puts the fear of God into one?" .)

I've seen this clue in the Evening Standard.

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