I am more hacked off by the assumption his extremely successful barrister wife does all the shopping than the fact he may or may not have got the figures wrong.
You can only eat so much food...
Breakfast: cereal for the kids. He'll eat at the commons, she'll pick up a takeaway.
Lunch: both out on expenses or subsidised or whatever. Kids eat at nursery (they are younger than I both thought).
Dinner: both adults are probably out 3 nights a week, and they have small children so I suppose they probably eat 'normal' food - pasta, fish pie, chicken.
It's not that much food. I think it's perfectly possible to do it on £80 for groceries (so not including booze, nappies, cleaning products, food eaten for free/subsidised/bought on the hoof/family lunches out on Saturday, etc). The amount of food that family has to put in a shopping trolley every week is tiny, compared to people who don't eat out or have to pay to eat out, take their own lunches etc.
That all said, I completely agree with the pp who said this 'pretend you're normal' schtick is completely unhelpful.