There are tiny examples dotted around - Dartford river crossing being one..if you really need to get across the Thames for free then drive between 10pm and 6am. Though I'm sure no-one is really doing that, Blackwall is free and just 30 mins up the river after all.
It does feel like a long-assed journey from the 1970s and the BR examples above, to now where the RDG / TOCs are still confusing passengers with a variety of fares. Flat rates obviously don't work for the railways and nor should they but it feels like the industry still has a considerable way to go and will require government legislation to make it happen.
Anyway, I'm straying dangerously into a Fares Advice & Policy rant. So.. how about all that polyester and that shiny Mk2 stock?!