Are there double yellows at the bus stop? Is it a marked bus stop? The angle of the photo makes it difficult to see the road to make a judgement. Which house were the police visiting?
Even if the van wasn't there I'd imagine it would be difficult for a bus to pull into the gap between the two cars.
It does say in the highway code not to park in a marked bus stop, but the same rule also says not to park facing against the traffic flow, and how many people do this on a daily basis.
I'm always willing to give emergency or other official vehicles the benefit of the doubt, especially if you don't know the circumstances, and whether they're exempt from the normal rules. I've often seen people whinge about traffic wardens parked on double yellows.
In this case I don't know what the police were doing, whether the use of the van meant there was equipment or people that needed to be close to where they were working, or whether the road was chock full of cars and it would have meant parking the police van some distance away.
I'd rather see them in the van and on their way to the next job than wasting minutes walking back to the van if it had to be parked streets away.
Heres a couple-- one of a well known car driving school waiting parked on double yellows for 20 minutes to pick up a school girl for her lesson and just for the record reg FP14 NFD. (not the first time hes parked there either) The other in Upton--no parking space-- no problem straight up on the pavement.