I wonder if he just doesn’t think he’s ever told me before even when he said it to me 40 seconds ago. Yes, this, precisely. I tell people things, then halfway through have a memory of telling this person the same thing, so I stop and apologise. He won't be getting even that memory.
He gets really sad about his childhood, it’s sad hearing him talking about and it upsetting himself and he does it over and over again. That's sad. Can you keep a stock of happier memories that you can bump him into? (Sorry, I'm back into the glitched record analogy, were you nudge the needle very slightly and it slips into a different groove)
I used to write things in big letters on the top of Dad's paperwork "No action needed, can be thrown away" "to be filed" "paid by cheque on "
Yes, he'll tell you not to bother with the housework because your doing it implies he's not up to it. I used to say to Dad that I know he can do it himself but this is just to give him a day off.
Probably it's more hygienic for him to cook than to prepare cold food 
Have you got PoA for Health and Welfare? Have you sent it to the GP? It must be difficult now, I was at the same GP as my father, so I made an appointment with a GP to talk about him. But now they have that on-line triage in place and it's difficult enough getting any sort of response for your own illnesses. Emphasise the drugs/safeguarding.
It is possible to get the drugs dispensed in a dosette box from the pharmacist, all neatly divided into days and time of day. If you could get that set up, it might be easier to sell it to him "Grandad, they've changed the way they're packaging drugs, they're doing it this way now".
Main thing GP and memory clinic will give you is a diagnosis. You might be better off tackling the symptoms - social services are the people to tap into, though they're just as pressured. Understate what you're able to do (anything you say you can do you'll be left to do 365 days a year, holidays and illness notwithstanding).