Op - you say but not sure we could ever stretch that far. - but the problem is, if you earn enough that your DC only gets minimum loan, or close to minimum, you will have no choice but to help, or make them work through 6th form and at uni (if they can get a transferrable job and their uni course allows time for a job).
We are in same position as previous posters, DS gets minimum loan, it doesnt even cover the accomodation cost. We are topping the loan up for halls fees (approx 1400 for the year) and then give him a monthly maintenance allowance. Effectively same as PP are doing, but a slightly different way.
DS had a retail job for past 18mths, managed to save a lot, did overtime etc, but not enough to live on without our contribution. He keen to get another job, but his course is a science, so pretty busy with labs etc and if we couldnt help (eg v high mortgage, lots other kids), he would struggle to earn enough to match our contributions. Fortunately we are also at stage of life where we can help (and only 1 other DC at home.)
I am sure you are not alone in not realising how much you may need to contribute. My colleague's eldest goes in 3yrs, both she and her DH have professional jobs, but having heard me mention the contribution needed by us, she is now panicking!! I obviously dont know her financial circumstances, but from knowing hers & her DH's occupations, I am guessing their joint salaries will mean they will need to contribute significantly.