Should have gone left as the signs all say

The signs that are posted at the junction, which is no use when there's
two lanes of traffic on your left (lane 1 turning left, lane 2 heading
straight on, lane 3 heading straight on, lane 4 heading right), traffic
behind you and the only way to go without causing a delay is to the
right.

The road you're talking about IS entirely residential
and I expect that is why it closes to straight-on traffic at night

The road is a green "Primary Route", a major thoroughfare for traffic
from the north of London to the south.

There are several symbols defined (dot in road, line across road,
yellow/purple dashes) to indicate a road with restricted access.