I agree with Back too.
I don't spend a lot on DS's packed lunches (nowhere near £400!
) so probably wouldn't notice any savings. I'm sure that what I send with him is healthier than he'd have at school. He's vegetarian and about 75% of the meals are Quorn-based. I really don't like the thought of him eating that much Quorn. His appetite can be quite up and down - when he's having a growth spurt, he'll eat masses and I'll pack his lunch accordingly and then pack less when he's not so hungry. Any uneaten food comes back so I know exactly what he's had.
Also, what's this going to do to family mealtimes? At the moment both DS and I have sandwiches at lunchtime so in the evening, I make a hot dinner (well, usually!) and we sit down at the table to eat together. If he's having a hot meal at lunchtime, he's not going to want a hot dinner so I'm going to eat by myself every night!
In short, I think I know better than the government about how to feed my son!