Tourists be warned: The Olympics crush has begun in London -- and so has the scramble for cold, hard cash in the pricey British capital.

Lines are getting longer at ATMs, visitors are in sticker shock over British prices and some befuddled tourists are wondering what currency to use. Stores in the Olympic Park only accept certain credit cards and a British financial authority is even recommending that tourists make sure to bring British pounds with them.

"I've had people asking me whether they should pay in British pounds or euros," said Alex Singer, a 27-year-old London cab driver. "I've also had Americans thinking that they can pay me in dollars."

Britain, which uses pounds -- not euros or dollars -- had a test run ahead of the Olympics last month when some cash machines in the city ran dry over a four-day holiday.

During Diamond Jubilee celebrations in June to honor Queen Elizabeth II's 60-year reign, dozens of ATMs across London ran out of cash as hundreds of thousands descended on the city to see fireworks, concerts and a flotilla of 1,000 boats on the Thames.

Some bars and restaurants even held on to drivers' licenses and other IDs as collateral so people could return with cash the next day to pay their bills.

An estimated 1 million extra visitors are expected in greater London during the Olympics, which begin July 27 and run through Aug. 12 -- a near three-week extravaganza as opposed to the Jubilee weekend.

"It's going to be chaos," said Zelda Buchanan-Clark, a London teacher. "They're going to have to carry extra money."

The U.K.'s Payment Council, which works with banks and other cash providers, says assessments have been made to figure out how much cash is needed in London during this tourist surge and what denominations will be most useful.

But it has also advised tourists to withdraw cash before they get to London and to have backup plans in case their credit cards are rejected or local cash machines run dry.

An estimated 49 billion pounds ($77 billion) of cash is in circulation across the U.K., and there will be 1,700 cash machines near Olympic venues, the Payment Council said.

"We've been working to make sure that there is enough cash to meet demand," said Michelle Whiteman, spokeswoman for the Payments Council. "But at any point in time, a cash machine may run out of cash. It's just that it will be more noticeable during an event like this."

Further complications may be in store for credit card users at the games. Since Visa holds an exclusive sponsorship for the London Olympics, people at Olympics venues will either have to use cash, Visa credit or debit cards or go to kiosks where they can use other credit cards to purchase a special Visa prepaid card.

Have all that?

Visa has also removed 27 ATMs from Olympic venues and replaced them with just eight Visa-only cash machines. The company says, however, it doesn't expect any problems due to its exclusive Olympic sponsorship.

"We've been sponsoring the games for 26 years and we've never had an issue with it," said Matt Kauffman, head of Olympic management for Visa Inc.

He said 98 percent of U.K. residents hold either a Visa debit or a Visa credit card, and that 80 percent of those attending the Olympics will be from the U.K.

Ample supplies of cash -- and credit -- will be needed as visitors grapple with London's high prices. The British capital has long been one of the world's most expensive cities and vendors are certainly not lowering prices before the games.

The basics are not cheap: a crosstown ride on London's overcrowded subway can cost up 4.80 pounds ($7.50 ) at peak times even with a discount travel card. A half pint of beer and a hamburger with fries in a typical pub costs about 10 pounds ($15.60). A single movie ticket at the Odeon in Leicester Square runs 14 pounds ($22).

Move into the luxury sphere and the prices become stratospheric. Afternoon tea at the historic Hotel Savoy costs 45 pounds ($70), then rises to 58 pounds ($90) if you add a glass of champagne. The tip is included, but that's little consolation.

Some say these could be called the sticker-shock games.

"I just paid nearly $11 for three small tacos," said Amanda Riley, a 23-year-old student from Minneapolis who has Olympic tickets. "That would keep me in tacos for two days back home! I'm going to go broke."