Barry Salter wrote:

The left-hand lane of Silver Street (entering towards the middle of
the frame) is now a bus lane, with a banned left turn onto the A406
Eastbound at the traffic lights, forcing any traffic wanting to join
the A406(E) to proceed across the lights, and all the way round the
roundabout. (Not that that stops people from making an illegal left
turn anyway, usually in front of a bus).

Are you absolutely sure that banned left turn is a new thing? I recall it
being put in when the underpass was built, to stop people going from from
the A10 s/b to the A406 e/b using Kendal Parade to bypass the roundabout.

The A111 (Hedge Lane), which comes off of the A10 (Great Cambridge
Road) Northbound at an approximate 45 degree angle, has been
converted from two way traffic between the junction with the A10 and
Taplow Road (the
road linking Hedge Lane and the A406 East) to one way, as has Taplow
Road itself, so traffic heading from the A111 onto the A10 (North) and
from the A406 (East) to the A111 (North West) or A10 (North) has to go
round the roundabout.

....although there would be very little traffic doing those turns anyway.