The limit was introduced to distinguish for grant purposes between students who might reasonably be expected to travel daily from their homes to college and those who might be obliged to incur additional costs by living away from home because of the distance involved.
Under the terms of the schemes of student support the lower adjacent rate of maintenance is paid without exception to every dependent grant-holder whose normal family residence is less than 15 miles from the college attended.
The adjacent rate of maintenance is also paid in the case of independent mature students whose normal residence while attending college is less than 15 miles from the college attended. The higher non-adjacent rate of maintenance is paid in all other cases.
I have no plans at present to introduce graded limits under 15 miles for the purposes of determining the appropriate maintenance grant.