Crawl with cops inside room (6,4)
I believe the answer is:
snails pace
'crawl' is the definition.
(both can mean a very slow pace)
'cops inside room' is the wordplay.
'cops' becomes 'nails' ('nail' can be a synonym of 'cop').
'inside' is an insertion indicator.
'room' becomes 'space' (I've seen this before).
'nails' put within 'space' is 'SNAILS PACE'.
'with' is the link.
(Other definitions for snails pace that I've seen before include "at a very low rate" , "Slow rate of progress" , "no rush" , "Very slow speed" , "making slow progress" .)