Heading to London in 2.5 weeks

Get cash when you arrive and use cash through out your trip. That's my advice.

You can withdraw money with a debit card at the airport, no need to arrive with local currency. Vendors at the airport take credit cards if you need a coffee before you get to the ATM.

I'd say bring some cash, even dollars, which you can change if needed, keep if not. Seen people stuck before because their cards were blocked. Tell your bank when and where you going. American Express is not really accepted here. Handy to have a few pounds on you when in town, but cards used mostly. Markets and similar places sometimes don't accept cards and it's common to have a £10 minumum spend to use a card in smaller shops. Have fun.

As a general rule, the best way of getting local currency is from an ATM at your destination. In my opinion, however, it's always a good idea to have some local currency in hand when you land. Getting two or three hundred British Pounds from your local bank will cost you a little more, but it eliminates the hassle of trying to find a machine, the stress of hoping it works (they do occasionally malfunction), and doing it all while somewhat jet lagged. To me the small amount extra it cost to have money in hand when arriving is money well spent, and the extra cost relative to the overall cost of the trip is not, in my opinion, that much. Just one point of view

I'd only get cash in advance if you know you're going to be worrying about it during the days before and the flight over. The main drawback of getting cash in advance is that the some banknotes have been changed out recently and you might end up with old notes that you'd have to exchange at the Bank of England. If you have Apple pay, you can use that as contactless for the every day small purchases, it's perfectly acceptable. There are the few situations where cash is better, I haven't seen a London pub that didn't accept card payments, but I have seen it in other UK cities. If you use a lot of cash, then you'll have a pocketful of coins and since you're not familiar with them, it can take some time to count them out. I usually start each morning with my one and two pound coins in one pocket, my 50 pence and 20 pence coins in the other pocket. I'll use coins to top up an Oyster card as well. My lower value coins tend to end up in donation boxes or given to buskers.

Find out from your bank if they have reciprocity with specified British banks like Barclays or HSBC in which ALL ATM fees are reimbursed vs just some. Don't make assumptions; verify what the reimbursements are.

beware of non-bank ATMs, these can charge significant fees. Bank backed machines have the Link logo. http://www.link.co.uk/atm-locator/

Thank you all for the reply's. Very informative. Do many places over there take Apple Pay? And what are Buskers?

A busker is a street musician.

If arriving at Heathrow T5 there's an ATM directly after immigration, you can't miss it.

We just got back from England and used our credit cards during our stay. I would carry some pounds with you and use them in places that normally do not take credit cards--these places are similar to cash only places in the US like food stands or some outdoor markets. We used a capital one credit card which does not charge you a foreign transaction fee which is different than an ATM fee.

beware of non-bank ATMs, these can charge significant fees. Bank backed machines have the Link logo. http://www.link.co.uk/atm-locator/

Over 50% of the ATMs in Link are operated by independents. Banks have largely quit the ATM business except at their own branches.