tim..... wrote:

(It's also the reason why the Dartford bridge was built as
the southbound lanes)

Huh?

As the toll booths are on the south side, a tail back
at the booths will queue onto the bridge and not into
the tunnel

Hehe, for some reason I thought the tollbooths were on the northern side.

Looking at the satellite photo, it looks as if you can get into the tunnel
without going through the tollbooths.