On reflection, I would start to assess boring haircuts, which is irregular (8)
I believe the answer is:
sporadic
'is irregular' is the definition.
(similar in meaning)
'on reflection i would start to assess boring haircuts' is the wordplay.
'on reflection' says the letters should be written backwards.
'i would' becomes 'I'd'.
'start to' says to take the initial letters.
'boring' means one lot of letters goes inside another (some letters must 'bore' a hole into other letters).
'haircuts' becomes 'crops' (crop is a style of haircut).
The initial letter of 'assess' is 'a'.
'id'+'a'='ida'
'ida' placed within 'crops' is 'cidarops'.
'cidarops' backwards is 'SPORADIC'.
'which' is the link.
(Other definitions for sporadic that I've seen before include "Having separate patches" , "Picadors being scattered, here and there" , "Isolated; intermittent" , "Occurring now and then - cop raids (anag)" , "Occasional - intermittent" .)