It doesn't matter. People live 7 days a week and in the 21st century should have access to healthcare 7 days a week. Not "emergency only" healthcare. Tescos will sell me a can of beans on a Sunday even when it is not an emergency. The NHS needs to provide a similar 7 day service. End of debate really.
Anybody who says "end of debate" shouldn't be allowed to participate in one until they go away and learn what a debate is.
Tesco's selling you beans or even that packet of Tampax you need on a sunday is entirely irrelevant unless you think that healthcare should be treated exactly the same as a retail commodity.
It's a position you're entitled to take but if that be the case you have the option of buying your own private healthcare for your grandad at private market rates, which I suggest you do.