How much hard cash for London and Lauterbrunnen?

First, always pay local bills with local currency (or credit card). If you try to use Euro in Switzerland or London, you are at the mercy of the vendor who will decide the exchange rate. It will never be to your advantage. Where I am going or landing I will have local currency equal to about 100 US. That will pay the taxi to the hotel, maybe something to eat, etc., Enough to get me started without the panic of having to find a functioning ATM at the airport. Then I acquire what cash I need from a local bank's ATM. I use cash primarily for small purchases or if I don't want to mess with the local credit card machine. It just depends on what you are most comfortable doing. I always inquire about cash payment especially at hotels. Often you can get a discount for paying in cash.

I spent last week in London and never needed cash. In fact, most places won’t accept cash. I would not get more than 20 pounds cash. You probably won’t even spend that. Contactless card payments is what is expected.

Agreed 20 pounds London is more than enough… I give to buskers, for tips, and buying snacks and bottled water at small markets. CC or Debit Cards are preferred these days.

Can’t speak for Switzerland. Have not been there since the 70’s.

I can only speak to London. We were there 3 years ago and never needed cash until we paid for the Stonehenge bus at the Salisbury train station. There was an atm machine there but other than that credit cards for everything.

When you say credit cards are preferred, does that mean Apple Pay works well?

I went to a cafe the other day and their card machine went on the blink just before I went to pay. The bill was about £25 and I needed to pay cash. Although I can go awhile without using cash, it’s always as well to carry at least enough to cover the price of a meal. That’s my guide wherever in the world I am.

I have never been to Switzerland so I can’t comment on there. The only people I know that have been there are skiers.

Save your euros for another trip as you will lose out on the conversion rate.

The 2 of us spent a week in London last month, and brought along £80 from a previous trip. Two of the £20 notes were the older, paper versions, which are being discontinued in favor of the new flexible plastic notes, which have some small, transparent panes on them. We made a priority of spending the paper bills, as banks required us having an account with them in order to exchange them for the newer versions, and we didn’t want to be stuck with having to go through machinations in the future, when merchants aren’t accepting them any more. One small restaurant was cash only, but a couple others were credit card only. We still had £60 left on our last day, and spent the final paper note at a deli before we headed to the airport for our departing flight.

Never did withdraw any funds from an ATM the entire week. Tap-to-pay credit card readers are prevalent throughout London.

Swiss trip 3 years ago, I did use some cash over several days, but less than 200 francs. I still have a 5 franc bill from that trip. Have not tried to use “foreign” currency where a country had its own money. if you anticipate returning to anywhere in the EU within the next 2-3 years, I’d suggest keeping your euros for that trip. If not, exchange them, or you’ve just got €250 in souvenirs.

Regarding Switzerland, keep in mind that many of the public toilets cost 1CHF to 2CHF. So, you may want to have coins for those.

200 francs is too much but 100 would be OK, and you need to make sure to break it into small change asap because that's really when cash is needed in Switzerland: toilets, lockers, farm stands/dispensers with honor-based payment...

I like to have enough local currency on hand that would cover a taxi ride to hotel and a meal, if necessary. But everyone has their own comfort level.

I have about 250 in Euros from a previous trip, would that help at all? Or would I get the stink eye from the Swiss?

Stink eye as in "sorry we cant take those"? Some places close to entry points might take euro, but unless you're going to be traveling in euro-zone countries again sometime soon, I'd take them and convert to CHF when you get to Switzerland just to get rid of them. Yes you will get hosed on the exchange rate, but you will anywhere. Same with any leftover pounds, again, unless you will be going back to the UK anytime soon.

As Cyn said, they change currency every so often over there, so if you hold onto them for several years, you could get stuck with old notes you can't use.

Yeah on this same trip I will be spending 3 weeks in France Germany and the Netherlands.

English is not my first language (neither the UK nor the US variant), so I would like to know:

What is the difference between "cash" and "hard cash"?

Wikipedia has the same definition as far as I can see :-(

You are right, exact same meaning. Just a colloquialism.

But for the OP, that 250 EUR cash will come in handy in France, Netherlands and Germany.