Attack official UK statisticians, chuckling with no sign of hesitation (9)
I believe the answer is:
onslaught
'attack' is the definition.
(an onslaught is an attack)
'official uk statisticians chuckling with no sign of hesitation' is the wordplay.
'official uk statisticians' becomes 'ons' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'chuckling' becomes 'laughter' (I've seen this before).
'with no' indicates named letters should be taken away.
'sign of hesitation' becomes 'er'.
'laughter' with 'er' removed is 'laught'.
'ons'+'laught'='ONSLAUGHT'
Can you help me to learn more?
(Other definitions for onslaught that I've seen before include "Assault" , "Violent attack" , "Sally" , "offensive action" , "Destructive attack" .)