Be slow to make a settlement in vile surroundings (3)

I believe the answer is:

lag

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'be slow' is the definition.
(to lag is to be slow)

I don't understand the rest of the clue.

(Other definitions for lag that I've seen before include "Dawdle" , "Insulate (pipes)" , "An old one is a convict" , "Old convict - dally - insulate" , "habitual criminal?" .)

I've seen this clue in the Evening Standard.

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