Before the fast, let there be a shopping spree.
From Harrods in Knightsbridge to the shining diamond shops in Mayfair, London has long drawn big spenders. But every year around the sacred 30 days of Ramadan, which has started weekend, a pattern of amazingly rich Arab customers comes and takes the retail store to a whole new level — complete with an entourage of security officers, staff, and Gulf-registered Rolls-Royces and Ferraris traveled in just for the occasion.

Retailers call the boost in business the Ramadan Rush: A greatly profitable and fast-growing market motivated by rich Arabs who travel to England to evade the desert heat and engage in buying high-class gifts before traveling back home for Ramadan and increased spiritual observance. Another increase occurs during the Eid holiday, which represents the end of Ramadan.

The raise in customers during summer season time has been so regular and recognizable on London’s roads that some have amusingly known as the pattern the “Harrods Hajj,” after the traditional Islamic pilgrimage to the sacred town of Mecca.

“London is the place in Europe where the Middle Eastern visitor shops the most. It is almost their second home,” said Gordon Clark, U.K. administrator at Global Blue, the Switzerland-based retail store research firm. The company reports that pre-Ramadan sales last July jumped 60 percent compared with the previous year.

Although visitors from the oil-rich United Arab Emirates, Kuwait, Saudi Arabia and Qatar create up only a tiny proportion of complete visits to Britain in contrast to those from the U.S. and European countries, they tend to be much more luxurious spenders. Official numbers show that Arab visitors rated just 19th in terms of numbers of people last year, but came second in total spend — 888 million pounds ($1.5 billion).

The Kuwaitis are the greatest spenders, paying out some 1,340 weight ($2,275) per deal last July, Clark said.

That matches with data from the London Luxury Quarter, a group that symbolizes some of the highest-end businesses in central London. It said the common investment from Middle Eastern customers last year came just behind the China, its top customers.

Ramadan falls on the ninth month of the Islamic lunar calendar. Muslims around the world fast from dawn to sunset for a month, started from Saturday.

All that may leave the average British or American consumer feeling a bit left out. But the Ramadan Rush does carry one direct benefit to the masses: Earlier revenue. Many of The Britains shops and fashion brands have been modifying their summer revenue routine to make sure the high paint rollers get to shop new stock when they appear.

“They’re not interested in revenue, because the shops are too busy,” Clark said. “It’s not a good purchasing experience for them.”