If this is a problem, write an app that emails/faxes/whatever a report to TfL? Could even integrate some CV stuff to read a license plate number from the phone's camera. This is the sort of thing that takes large organisations a while to build, but could be a weekend project for an interested developer.
Still would need to be popularised to actually give any benefit (i.e. similar levels of accountability for minor shittinies as uber's ratings). people are lazy. Rating an uber takes seconds, and is built in to same app you need to order it. I am guessing many people don't rate anyway. Also, making an app that that does this well is NOT a weekend sized project.
