Cannot tell you where it is but it's an absolute shambles. Particularly for tourists. You hopping along on the M50 and are supposed to read signs that there is a toll up ahead and are given messages about a web where you can pay. I guess the tourists are going to stop the car and write that down. I think there's also a phone number and an option of paying at fourcourts (explain that to a tourist) etc. Blink and you'll have passed it without even knowing it. Every single time I've passed it in the last couple of years the messages are slightly different. Luckily I'm in a rented Hertz car and the toll is billed to my Amex account with no extra admin charges.