I used this both ways on 12th July and totally forgot to pay online afterwards. Today received two Penalty Charge Notices and went online to pay. It has taken payment but instead of the £38 each way it has only taken a total of £6 - is this because its a 'first offence'? Or do I have to pay the rest somehow?
Having looked again at the penalty charge notices the first one does indeed say something to the effect of as its the first notice issued for this vehicle then its possible to pay the crossing charge only, but the return journey letter only says about setting up an account - but the crossing charge was taken for both journeys with reference numbers for both notices on the receipt but no penalty so it looks like I have got away with it.
Exactly the same thing happened to a colleague a few months ago – so it would appear standard practice.
The government originally said that the Dartford crossing charges would be scrapped once the build costs had been paid for in crossing fees – the income from the fees exceeded the build costs some years ago – but the government decided that it was on to a good thing to keep charging (like a 10 year bank loan that you end up paying back forever).