jaramat
Well, there isn't a dedicated space for the barrow either, really. It actually blocks an entire column of shopping trays space when it's there, though it's not like we ever need that much space anyways.
It just seems so dangerous and impractical to me to have the barrow in the cabin where it could go flying in case of a crash. Also, to have to go around the car and back each time you need the barrow, which we pretty much always do since the average shopping is around 30-50 kg (I'd guess) and we carry the trays into apartment buildings.
Also, I just noticed - is the van a side- or a back-loader? Because if it's a sideloader, isn't the shutter supposed to be on the other side since it's a RHD?
We have the same situation with placing the barrow, where it uses up a whole column. 90% of the time, that space isn't needed, but when it is needed, we have to simply place the barrow on its side, meaning it slides about, which usually doesn't pose an issue when the side shutters are down, but unless you're careful, an unsecured barrow can cause a lot of damage. I do agree with you regarding keeping the barrow in the cabin though, I feel it's less safe.
These Sainsbury's vans are a back-loader type, much like vans used by other companies like Morrisons and Ocado.

In my opinion, it seems far less efficient with the back-loader layout as apposed to our layouts at Tesco, all that wasted space used for an area to actually walk into the compartment. Moreover, these Sainsbury's vans are slightly shorter in length, which is great for navigating tight streets in cities, but it does limit how much cargo you can carry. As far as I know, only Tesco and ASDA use the side shutters/doors layout, here in the UK.