Thanks to everyone for their responses. I’ve searched the various dongle providers sites…some do mention the non-use levy, some don’t…it’s a ‘gotcha’ hidden in the T&C’s. The first firm that does away with the charge will make a song & dance about it I am sure!!
Cheers, Dave
Maybe - but they have already started this process with the A13 out of Paris towards Normandy, and I think also an autoroute in the East - no more toll plazas just overhead camera gantries.
You will still be able to use a bipper which will be detected automatically, but without one you will either have to set up an account and register your car number plate, or have to remember to go and pay online within 72 hours of your journey.
https://www.autoroutes.sanef.com/en/my-journey/toll-a13-motorway
Same idea as the Dartford Crossing in the UK.
Thanks for the replies everyone. I’ll take a close look at the Ts&Cs for the providers.
And just look how much that has earned them with people forgetting. Millions!
Quite probably.
I’m not advocating for the new system, just mentioning its introduction.
I imagine that there will be a saving in not having the toll plazas - but it will also speed up traffic which is a benefit to the rest of us.
Yes but I like being special, privaleged, and sanctimonious with my tag as I leave the peasants at the tolls. 
Bip&Go for me. I had a bad experience setting up Ulys & it cost me a further €30 in charges plus the return postage from the UK at the time. Been with Bit&Go 2 years now & only get charged for using it. It’s great when you go straight through the tolls at <30kmh. They bill you at the end of each month too which is great.