In London, there are several payment methods available for making purchases. Here are some commonly used payment methods in the city:

1. British pounds in cash: It's always useful to have some cash on hand for small expenses, such as at local markets or for paying tips. You can exchange money at banks, currency exchange offices, or ATMs available in the city.

2. Debit and credit cards: Debit and credit cards are widely accepted in most shops, restaurants, hotels, and other commercial establishments in London. Make sure you know your PIN if you're using a debit card. Also, be aware of possible international transaction fees your bank may charge for using your card abroad.

3. Contactless payments: Contactless payments are widespread in London. You can pay contactlessly with a debit card, credit card, or even with your smartphone (for example, using Apple Pay or Google Pay). This is convenient for quick and easy payments, especially when using public transportation, such as the subway or buses.

4. Mobile payments: Mobile payment apps like Apple Pay, Google Pay, and other digital wallets are also accepted in many shops and restaurants in London. You can add your debit or credit card to the app and easily pay by holding your mobile device near the payment terminal.

Note that some small shops, market stalls, or local eateries may only accept cash payments, so it's always handy to have some cash with you. Additionally, it's advisable to always be vigilant against possible skimming or fraud practices and keep your cards secure.

It's useful to know that most places in London also accept payments in other currencies, such as euros or US dollars, but you should be aware that exchange rates may not be favorable. It's usually best to pay in the local currency (British pounds) to get the best rates.