Insecure mutt? (3)

I believe the answer is:

cur

I believe this is a double definition.

'insecure' is the first definition.
(in the letters 'seCURe')

'mutt?' is the second definition.
('cur' can be a synonym of 'mutt')

(Other definitions for cur that I've seen before include "Lowly dog" , "Useless dog" , "Scoundrel; mongrel dog" , "Surly dog (or person)" , "Dog of low breed" .)

I've seen this clue in the Evening Standard.

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