From Longman Dictionary of Contemporary Englishnot in the slightestnot in the slightestBritish English spoken not at all ‘Did he mind lending you the car?’ ‘Not in the slightest.’ → slight
Examples from the Corpus
not in the slightest• I challenge you to name an artist who is completely original, and not in the slightest bit derivative.• Shoddily made and prone to virtually instant disintegration, it's not that cheap and it's not in the slightest cheerful.• Of course, Alexander would not in the slightest deny the more traditional view. 