Given 3 hours per charge time of iPhone 5s, and 0.1 pence cost of doing so, we have a daily cost, at full utilization, of 0.008 GBP per vestibule per day. Assuming 2 vestibules per car, and a car in constant operation, with the outlet constantly occupied by a charger, we're looking at a cost of roughly 5.84GBP per car per year. Given the overall car maintenance and railway operation costs, that's noise not worth paying any attention to.
Any "solution" to this imaginary "problem" will cost more than this. Even having someone qualified write a report as to why a solution is unnecessary will cost more than the yearly cost of electricity here.
TL;DR: Making a problem out of this makes one look very, very dumb.