Would be nice if driving instructors (or at least mine) would have said it causes damage sitting with your foot on the clutch. Taught to put handbrake on when you're expecting to wait like at traffic lights (and possibly to put it in neutral, can't remember tbh) but after passing just ended up sitting with feet on the pedals out of laziness. Will make sure I put it in neutral from now on.
Problem is there are a lot of "instructors" in the system who are not actually fully qualified and are instructing on a "Pink licence" instead of a full licence. The system really needs changing, problem is there is a lot of money being made out of training instructors.
Use of the parking brake is covered in "Driving the Essential skills" which is the syllabus for learning how to drive. In the parking brake section it covers it's correct use, which is what the instructor should instruct to.
Also instructors are periodically graded 6 being the highest. Only around 6% are at grade 6. Though there are rumblings the grading system will be changed at some point.
Grade 6 - A very high standard with no significant instructional weaknesses.
Grade 5 - A good overall performance with some minor weaknesses in instructional technique.
Grade 4 - Competent performance with some minor deficiencies in instructional technique.
Grade 3 - Inadequate overall performance with some deficiencies in instructional technique.
Grade 2 - A poor overall performance with numerous deficiencies in instructional technique.
Grade 1 - Overall standard of instruction extremely poor or dangerous.
Grade E - This is a grade 1, 2 or 3 but if you have been teaching for less than 1 year you get given an E (educational) grade and a kick up the backside.
Plus it's easy to allow poor driving habits creep without even realising, when you're left to you own devices.