I don’t think your DH is right in that it’s not an average UK household spend but it certainly isn’t massively unusual and plenty on here (me included) saying they spend similar a month. In fact ours is more (2 adults two very hungry sporty teenage boys both over 6ft3 in the house).
From what you have said and without a full breakdown I’d suggest making some simple changes first, seeing what you spend over the next two or three months then dialling back more if needs be.
Go to somewhere cheaper to bulk buy the basics- maybe Lidl/Aldi or Costco/home bargains etc. This is for dry pasta,rice, washing powder, loo roll, all purpose cleaning spray etc
Buy meat in bulk, ideally reduced and freeze it. You can make bigger savings by going to farmers or cheaper supermarkets but it wanting specific welfare etc then look at end of the day Saturday in Waitrose and snap up packs of mince etc when near to use by date.
Also for meat do mince, whole chickens etc and stop any purchases of expensive cuts.
Bake your own cakes. Stop buying any snacks or biscuits or little nibbles and make two big cakes a week (or whatever your family needs). This costs me very little but means there is always something to satisfy a sweet tooth with a cuppa or end of a meal - my lot could eat an entire multipack of biscuits in one sitting and it all adds up
Buy larger pots of eg yoghurt not fancy min pots like muller corners. Make compote from frozen berries.
everyone drinks water and don’t buy any fizzy drinks or fruit juices. If needs be get some cheap squash.
Make two evening meals a week cheaper ones eg big pasta bakes, jacket pots with all the toppings. It’s so much cheaper, no one notices, it’s also quick to cook so win win
Look at lunches and breakfasts and cut out the expensive stuff like cereal.