It might work for newer Diesels but MB IDIs in the US don't prime when you unlock the doors. Is that only to reduce the amount of work if you realize what you did before starting the engine? Is it customary in the UK to lock the vehicle while fueling?

How does that device prevent putting the wrong spout in the filler neck? US pumps use the same spout for both. The difference is gasoline/petrol supply hoses incorporate a vapor recovery feature. They'll pump into a Diesel filler neck as long as the spout is properly inserted.

I see this a lot on TV these days - "The Station" - New Audi Commercial - YouTube

Sixto
87 300D