In short
About 20 minutes of the UK practical test where you follow a sat-nav or road signs without step-by-step examiner instructions.
Independent driving is a section of the UK practical test, roughly 20 minutes, where the examiner stops giving turn-by-turn directions. Instead they either set up a sat-nav (a TomTom Start 52) with a route, or ask you to follow road signs to a destination.
Missed turns are not penalised — only an unsafe reaction to one is. The examiner is testing your ability to plan ahead and read the road environment.
Related terms