Silly me, admitting grand acts of theft (8)

I believe the answer is:

muggings

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'acts of theft' is the definition.
'muggings' can be an answer for 'acts' (mugging is a kind of act). I'm not certain of the 'of theft' bit.

'silly me admitting grand' is the wordplay.
'silly me' becomes 'muggins' (I am not sure about this - if you are sure you should believe this answer much more).
'admitting' indicates putting letters inside.
'grand' becomes 'G' (G is short for ground as in a thousand).
'muggins' enclosing 'g' is 'MUGGINGS'.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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