It's crap OP and the government could do something about it.
I agree to using Olio etc and don't be scared to ask friends / neighbours, most of us have been in similar situations and are happy to help.
Ignore people telling you to change supermarket, my carer lives virtually next door to an ASDA it makes sense for him to shop there or the Iceland near by.
If you can extend your budget to £40 Iceland deliver for free but I know that might be a few months away.
Do you have a Sikh temple or mosque near by?
Langar is usually referred to as a community kitchen or meal set up to feed anyone for free. Depending where you are you can go for a free meal (you have to sit on the floor) if you are somewhere with a large Sikh population you may find you can get a food delivery,
My local one even provides Xmas presents for children who wouldn't get them otherwise.
Muslims have an obligation to help people known as Zakat, it's treated like a tax, now some funds only help other Muslims but some do general feeding of people A lot of Muslims who own take aways will give away some food, it's Ramadan at the moment so you may find a public iftar you can join.
I know not everywhere in the UK is so multicultural so if these are not options I understand.