Also, the ultimate dunking biscuit
30 second Peter Kay link, SFW
In discussing biscuits in depth I’ve found this site incredibly helpful. It hasn’t been updated for about 10 years, but remains a standard source.
The search box leads to more than 200 results on digestives.
Funny, but in reality, the Hobnob is one of the worst for dunking. According to rigorous scientific testing the best dunker is the Bourbon.
Is that the one in north west London? I had my first holiday job there many years ago, on the production line! I remember the baking aroma which used to (and still does) hang over the neighbourhood.
I would guess that was added to make them rise a bit. Otherwise you’d be eating digestive hardtack.