I've been thinking about this further.
Without a doubt, as said, some children usually have their only meal at school and their family don't feed them unfortunately. These are extreme cases and sadly there are lots of them. This situation though is beyond a money issue. Parents who do not feed their children any meals a day are essentially negligent. Chances are, if they have £15 a week, they will remain negligent because the lack of feeding their kids is beyond money. Receiving lunch and possibly breakfast when at school is good because the kids actually get food. Food parcels mean food is in the house and although it might need preparing, there is actually food.
More people who receive free school meals do feed their kids when they're not at school. They might struggle financially and one less meal or a main meal they don't have to find is really helpful. The vouchers will allow them to keep their kids fed as they have before.
The trouble is, there are children who fall into both categories. When children aren't in school some probably won't get fed even if vouchers are provided and sometimes even if food is provided direct. These seem like social service issues to me and often they are already involved but not always.
I do t know what the answer is. But for kids whose families in normal circumstances don't feed them at all..I really don't think vouchers will be the answer, even if they are for lots of money. The issues are so much bigger.