I was coming out of Windmill Road, heading South after the traffic lights turned green. To turn right onto the A4 you have to drive over one box junction on the East bound carriageway to get to the middle where you can then wait and turn right onto the West bound carriage way (via another box junction).
The car in front of me was also turning right so I slowed to give it some space with my back wheels in the first box. The bus coming the other way and the cars behind the bus then blocked the West bound right turn meaning. I could have pulled further forward, right up against the car in front, but didn't feel it was necessary - there was space as can be seen in the picture. The car in front also could have pulled further forward, into the West bound box junction, as you are allowed to enter a box junction when turning right.
My understanding is that it is OK to enter a box junction to turn right, which is what I was doing. It is complicated by the fact that there are two that you have to drive through with a break in the middle. If it were a single box, I would be fine to enter to turn right. I also feel the timing of the image is misleading - the bus was there at 19:37:53, it is gone 4 seconds later and the car in front of me is just about to turn right. The white van behind me has caused the issue as the Audi cannot turn right Eastbound, which prevents us from turning right Westbound.
Street view:
https://maps.app.goo.gl/MHgkFr1uRegYN1T36https://tfl.gov.uk/modes/driving/view-pcn-details?pcnId=GX27135721&vrm=MT65TWD&journey=View&skippedIssuedPage=truePCN: GX27135721
Number plate: MT65TWD
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