Period in which Press Association guides electorate initially (4,3)
I believe the answer is:
iron age
'period' is the definition.
(prehistoric period)
'press association guides electorate initially' is the wordplay.
'press' becomes 'iron' (ironing is a kind of pressing).
'initially' suggests taking the first letters.
The initial letters of 'association guides electorate' is 'age'.
'iron'+'age'='IRON AGE'
'in which' is the link.
(Other definitions for iron age that I've seen before include "Period in the history of man - a region (anag)" , "It followed the Bronze Age" , "Very old period" , "Hist. cultural stage" , "A region (anag) - period long ago" .)