Too busy folk holding policemen back (7)
I believe the answer is:
besides
'too' is the definition.
(I know that too can be written as besides)
'busy folk holding policemen back' is the wordplay.
'busy folk' becomes 'bees' (busy as a bee).
'holding' indicates putting letters inside.
'policemen' becomes 'dis' (DI's, detective inspectors).
'back' shows that the letters should be reversed in order.
'dis' in reverse letter order is 'sid'.
'bees' going around 'sid' is 'BESIDES'.
(Other definitions for besides that I've seen before include "also is available" , "In addition, as well" , "See bids (anag)" , "What's more" , "Moreover" .)