Infernal creatures covering Harry head to toe (10)

I believe the answer is:

hellhounds

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'infernal creatures' is the definition.
(I've seen this before)

'covering harry head to toe' is the wordplay.
'covering' means one lot of letters goes inside another.
'harry' becomes 'hound' (both can mean to harass).
'head to toe' becomes 'hells' (I can't justify this - if you can you should give a lot more credence to this answer).
'hound' put within 'hells' is 'HELLHOUNDS'.

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(Another definition for hellhounds that I've seen is " Infernal creatures".)

I've seen this clue in The Independent.

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