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London is one of the most expensive cities in the world: getting around is expensive, eating can be pricey, travel costs are steep, and hotels aren't cheap. However, for every yin there's a yang, and travelers do get a break in other places: most museums are free, for example, and Oyster cards help cut the price of travel.

ATMs and Banks

Your own bank will probably charge a fee for using ATMs abroad; the foreign bank you use may also charge a fee. Nevertheless, you'll usually get a better rate of exchange at an ATM than you will at a currency-exchange office or even when changing money in a bank. And extracting funds as you need them is a safer option than carrying around a large amount of cash.

PIN numbers with more than four digits are not recognized at ATMs in many countries. If yours has five or more, remember to change it before you leave.

Credit cards or debit cards (also known as check cards) will get you cash advances at ATMs, which are widely available in London. To make sure that your Cirrus or Plus card (to cite just two of the leading names) works in European ATMs, have your bank reset it to use a four-digit PIN number before your departure.

Credit Cards

Remember to inform your credit-card company before you travel, especially if you're going abroad and don't travel internationally very often. Otherwise, the credit-card company might put a hold on your card owing to unusual activity—not a good thing halfway through your trip. Record all your credit-card numbers—as well as the phone numbers to call if your cards are lost or stolen—in a safe place, so you're prepared should something go wrong. MasterCard and Visa have general numbers you can call (collect if you're abroad) if your card is lost, but you're better off calling the number of your issuing bank, because MasterCard and Visa usually just transfer you to your bank; your bank's number is usually printed on your card.

If you plan to use your credit card for cash advances, you'll need to apply for a PIN at least two weeks before your trip. Although it's usually cheaper (and safer) to use a credit card abroad for large purchases (so you can cancel payments or be reimbursed if there's a problem), note that some credit-card companies and the banks that issue them add substantial percentages to all foreign transactions, whether they're in a foreign currency or not. Check on these fees before leaving home, so there won't be any surprises when you get the bill.

Before you charge something, ask the merchant whether he or she plans to do a dynamic currency conversion (DCC). In such a transaction the credit-card processor

Dynamic currency conversion programs are becoming increasingly widespread. Merchants who participate in them are supposed to ask whether you want to be charged in dollars or the local currency, but they don't always do so. And even if they do offer you a choice, they may well avoid mentioning the additional surcharges. The good news is that you do have a choice. And if this practice really gets your goat, you can avoid it entirely thanks to American Express; with its cards, DCC simply isn't an option.

Credit cards are accepted virtually everywhere in London.

Reporting Lost Cards

American Express. 800/528–4800; 01273/696–933; www.americanexpress.com.

Diners Club. 800/234–6377; 514/877–1577; www.dinersclub.com.

MasterCard. 800/627–8372; 0800/964–767; www.mastercard.com.

Visa. 800/847–2911; 020/7795–5777; www.visa.com.

Currency and Exchange

The units of currency in Great Britain are the pound sterling (£) and pence (p): £50, £20, £10, and £5 bills (called notes); £2, £1 (100p), 50p, 20p, 10p, 5p, 2p, and 1p coins. At this writing, the exchange rate was about Australian $1.79, Canadian $1.76, New Zealand $1.97, U.S. $1.56, and €1.25 to the pound (also known as quid).

Even if a currency-exchange booth has a sign promising no commission, rest assured that there's some kind of huge, hidden fee. (Oh … that's right. The sign didn't say no fee.) And as for rates, you're almost always better off getting foreign currency at an ATM or exchanging money at a bank or post office.

Banks never have every foreign currency on hand, and it may take as long as a week to order. If you're planning to exchange funds before leaving home, don't wait until the last minute.