Cash or credit card preferred for purchases in London

We traveled all over UK and Scandinavia over the last two years. I did not see a single Krone used at any place in Scandinavia. I did once have need of a coin to use a public toilet in Scotland.
Use pounds and pence if you want to; but, you could probably live in these countries for many months without need for cash. Further, if cash is required just use an ATM near a bank.
I never use cash in the US. This is just how I do things. You should do what you feel comfortable with.

I was just there for 6 weeks. Tap credit or debit card used everywhere.

I was there in October and it was difficult finding anyone to take cash. Had a bit left over from previous trips, taxi drivers would accept it.

In November I used nothing but Google Pay for everything I bought in London - transit, restaurants, groceries, a little bit of shopping. I didn't even take my credit card out of my wallet. I had some change from a prior trip with me, but I wound up dropping it all in a leftover currency bin at Heathrow.

The only place that I needed to use cash on my last trip to the UK was at a laundromat where the attendant gave me change for a 20 GBP note so I could use the coin-operated machines. On the prior trip, I only needed cash once to buy a bottle of water at a kiosk.

There are very few cases where cash is needed.

Virtually everything is either credit/debit or some other electronic method, as others have mentioned. We took out 40 pounds cash for our 2-week trip to Scotland and London, and I only needed it a few times, although I was glad to have some coins for a pay toilet outside the Tower of London!

I use credit cards (usually via Apple Pay) all over Europe and the UK and never have had a a problem. I was in England this year for 6 weeks and used credit cards for every transaction, except one.

I've been in the UK for six of the last seven months.

I've used cash four times--three of those were to get a haircut and the last was for a taxi.

I pay for almost everything with Google Pay.

I would suggest having a few pounds just in case but not many. You could probably wait until you get there to hit up an ATM.

Ditto the others. A week into my current trip and I’ve yet to use any cash.

I live here and carry a wallet with a £10 note and one card. Just in case, but they never get pulled out. I never take my wallet out.

The last cash I used was - actually I really don't remember. I don't carry coins.

I use my iPhone with Wallet. For. Absolutely. Everything.

In the last 5 years I have taken money out of an ATM 4 times - £70 towards the end of 2019 included paper notes which have since become unaccepted so I used them and withdrew £50 in 2022. I still have all of that money.

I also took out some Euro about 3 years ago in the Taunus region of Germany and used some of that. I got 200 CHF in Bern in 2019 and have used some of that.

Whilst all of the posters above are correct in that it's perfectly possible to visit and not use cash at all the situation for locals across the country can be a bit more mixed. I use cash every week for a few things. I have someone who delivers eggs to us who only takes cash. The local Chinese takeaway will only take cash. A cafe I often visit when out cycling will take cards but prefers cash.

Use of cash in the UK has actually gone up in the last year.

When I visit a free-to-enter church for the purpose of sightseeing, I like to drop some money in the donation box. There's not necessarily going to be a way to donate via credit card. As already mentioned, I'd be concerned about running into a cash-only public toilet if I had no coins available. In addition, you never know when you'll run into a stand at a street market that doesn't take credit cards. That wouldn't usually be a mission-critical purchase, but I like to have a small amount of money with me, no matter where I'm traveling. If traveling only in major metropolitan areas, I'd probably settle for getting 20 pounds out of an ATM. It spending time out in the countryside, I might want a bit more, because I wouldn't know how easy it would be to find an ATM.