Yes it is, and a look reveals that you had passed the give-way line on your side of the bridge when the approaching vehicle, (that you couldn't see due to the bulk of the Waitrose van) had only just turned in to Salter's Hill. The council's position is that you should give way when a vehicle enters Salters Hill from the other direction which is total tosh. The give-way length is that lying between the give-way line on your side, and this sign on the other side: -
https://maps.app.goo.gl/JSTvgzG6pRg75iZz8This is just under 38 metres, and the distance from the give-way line to the entrance to Salters Hill from Gypsy Road is just under 79 metres, so there is 41 metres between the entrance to Salters Hill from Gypsy Road to the sign giving precedance. The speed limit here is 20 mph. As you can see, they deliberately use a camera that squashes the perspective.
However, you can only test the matter at London Tribunals because this is such a 'nice little earner' they refuse all representations to make sure the money rolls in. They know that >95% of people getting a PCN here just cough up to get t h e discount, not knowing the law on locations like this, that are all over the UK, but ruthlessly enforced only in Lambeth.
What I suggest is you look at the London Tribunals Statutory Register using Salters Hill as your search argument and look at the cases than come up.
https://www.londontribunals.gov.uk/about/registers-appeals
