Annoying girl fills in old Tax Office books (8)
I believe the answer is:
irritant
'annoying' is the definition.
(I've seen this before)
'girl fills in old tax office books' is the wordplay.
'girl' becomes 'rita' (woman's name).
'fills in' is an insertion indicator.
'old tax office' becomes 'IR' (Inland Revenue, predecessor of HMRC).
'books' becomes 'NT' (abbreviation for New Testament).
'ir'+'nt'='irnt'
'rita' placed within 'irnt' is 'IRRITANT'.
(Other definitions for irritant that I've seen before include "Annoying thing" , "Something that annoys, a nuisance" , "Annoying factor" , "Something that chafes or annoys" , "Something that causes annoyance and bad temper" .)