Confused impression of British Library upper limits (4)
I believe the answer is:
blur
'confused impression' is the definition.
(I've seen this before)
'british library upper limits' is the wordplay.
'british library' becomes 'BL' (abbreviation for British Library).
'limits' means to remove the middle letters.
'upper' with its centre taken out is 'ur'.
'bl'+'ur'='BLUR'
'of' acts as a link.
(Other definitions for blur that I've seen before include "Muddle" , "This Brit-pop band is a bit hazy" , "Make or become indistinct" , "murky spot" , "Hazy or indistinct representation" .)