Any question answered...

In addition to the previous answers, the Wikipedia article says this:

The tunnel has several sharp bends, in order that the tunnel could align with Northumberland Wharf to the north and Ordnance Wharf to the south, and avoid a sewer underneath Bedford Street. Some sources state an additional purpose was to prevent horses from bolting once they saw daylight. The tunnel carries two lanes of traffic, though higher vehicles need to keep to the left-hand lane so that they do not hit the tunnel's inner lining.

[...]

In contrast with the Victorian northbound tunnel, the eastern tunnel had no sharp bends

https://en.wikipedia.org/wiki/Blackwall_Tunnel

The Bedford Street mentioned doesn't seem to exist any more.