But why would someone who hasn't used the crossing for years and didn't even know the system had changed have had a Dart Tag, even if they were still available?
And my memory of the Dart Tag ws that you had to drive through the lane fairly slowly while your tag was read (based on the delay between entering the booth lane and the barrier lifting).
So we are back to somebody suddenly braking to a crawl in the middle of fopur lanes of fast moving traffic. Of course, someone who went through too fast for the tag to be read would incur a penalty charge because they would be caught by the ANPR system, so it's a lost cause however you look at it.
Much easier to register for automatic payment even if you rarely need to take advantage of it.