Pay the Dartford Crossing charge (Dart Charge)
If you are planning a trip and it means going over the Dartford Crossing beware of paying though websites that charge you extra for their services.
Use the direct link above and pay £2.50 per crossing via the official gov website.
I googled “dartford crossing” clicked on top result and nearly paid £7.50 per crossing – fortunately twigged just in time this was a third party site charging an additional £5 per crossing!!