All learner drivers should know that they can't break the speed limit and expect to pass the driving test, but it is not just speeding that you need to avoid.
You could be failed on the driving test for driving too slow as well.
The DSA examiner is assessing your use of speed in different conditions, so while the speed limit on a street might be 30MPH, you as a learner driver need to know if it is safe to drive at that limit considering the prevailing road conditions. Is it a busy high street with people walking about, cars parked on the left and right, buses stopping and moving off, all these factors will affect the speed that you drive at, so you might need to drive at a slower speed than the posted limit.
Making progress on the driving test
The DSA driving examiner also wants to see you making progress on the test, so your speed must be close to the limit if it is safe to do so, as you don't want people trying to overtake you when it is not safe.
This is one of the reasons why the examiner will fail you for driving too slow on the driving test even if it is a multi-lane National Speed Limit (NSL) dual carriageway and you are doing 50MPH.
Can you guarantee I will pass driving test?
Listen to DSA instructor advice.
10 reasons people fail the driving test in the UK.
Stalling the car during the DSA practical car assessment.