Presume army reservists are asked to reassemble (4,2,4)
I believe the answer is:
take as read
'presume' is the definition.
(I've seen this before)
'army reservists are asked to reassemble' is the wordplay.
'army reservists' becomes 'ta' (Territorial Army - British army reservists).
'to reassemble' indicates an anagram (I've seen 'reassembled' mean this).
'are'+'asked'='areasked'
'areasked' anagrammed gives 'keasread'.
'ta'+'keasread'='TAKE AS READ'
(Other definitions for take as read that I've seen before include "Presume" , "Accept (something) without discussion" , "Suppose" .)