I only use coins for parking and only if there is no app covering that car park or they don't offer contactless at the machine. 80 or 90 percent do offer it where I park. I have to go to the local hospital frequently and the main car park offers both pay by app and contactless in addition to cash so I only use cash there if the machine has gone west. The smaller car park only accepts cash so cash it is there.
In addition to parking I'm hard pressed to think of another need for coins.
Notes (bills) get used maybe once a month or so somewhere or other but I can't off the top of my head remember where recently. Wait, yes I do. I needed a couple of things at an Aldi supermarket about 2 months ago and their power had gone off so no cards or apps accepted until the power came back on. But they had a till drawer open and some sort of backup to note what had been bought and I handed over a £10 note and got actual change back. Exceedingly rare.
Pretty much everything else in my life is on my phone - all my banking, bills, and payments as well as store transactions. Apple Pay and contactless is wonderful. When I go to the department store everything goes on Apple Pay. Even a 4K TV and laptop last winter. Just pay with the thumb.
The other thing is I'm not in London all the time - living as I do in the wilds of Northamptonshire - and the same in London applies here too. Today I was in rural Shropshire near the Welsh border and paid for everything there with my phone.
Then again, I don't need to worry about currency exchange, or only having a magnetic strip on my card. I guess only having a magnetic strip on my card would be a great reason to use Apple Pay or Google Pay.