A princely sum

But now the Opal Lounge has cemented its reputation further as the favourite playground for royal princes.

Crown Prince Moulay Rachid of Morocco is the latest in a long line of blue bloods to have made the city-centre style bar his drinking den of choice.

The prince partied with 20 guests last weekend, spending more than 1000 on alcohol in just four hours at the George Street bar.

Bar bosses had to step up security for the prince and his entourage when they were informed that he would be popping in for drink.

The 24-year-old prince, who is second in line to the Moroccan throne, was in Scotland for a three-day golfing trip to Gleneagles. He joins Prince William as the latest royal visitor to the night club.

His Royal Highness needed 28 of the 65 rooms at the Glasshouse hotel next to the Playhouse, at a cost of 11,000, to cope with his guests and luggage.

The prince, who is president of the Moroccan Royal Federation of Golf, also led Morocco’s candidacy to host the 2006 soccer World Cup, a battle eventually won by Germany.

The crown prince’s group spent their time at the Lounge drinking Moet & Chandon champagne, Absolut Vodka and Johnnie Walker whisky, washed down with a range of cocktails and shooters.

He even "generously" tipped waitresses and doormen before leaving.

David Hall, general manager for the Opal Lounge, said that customers were stunned when they realised they were drinking alongside royalty.

He added: "The prince had informed us prior that he would be arriving with 20 guests, so we knew that we had to keep security tight and look after him.

"He was very polite to everyone and generously thanked the staff for their fantastic hospitality.

"He said that he had a wonderful time and told us this was his favourite bar in Edinburgh. He said he would definitely be back when he is next in the city."

The Opal Lounge was created in 2002 after Montpeliers (Edinburgh) Ltd spent more than 2 million radically transforming the basement of the former auction house.

The 800-capacity club was designed by Malcolm Fraser Architects and has been billed as "quite unlike anything else in the city".

Montpeliers snapped up the former store rooms of the Lyon and Turnbull auction house, a B-listed building dating back to 1826, after it closed down five years ago.

Prince William last year famously invited younger brother Prince Harry up to Scotland to sample his favourite Edinburgh watering hole.

The pair were seen ordering pints of cider and downing the cheekily named Sex on the Beach cocktails.

Prince William, 22, likes to spend his own time in the city, as well as attending official engagements. He was again spotted at the Opal Lounge recently where he spent the whole night with a party of friends.

In November last year, police were forced to cordon off George Street as hundreds of people flocked to see dozens of stars arriving at the Opal Lounge for an after-show party following the MTV Awards.

The exclusive event attracted a list of top names including Justin Timberlake, Christina Aguilera, Pink and Dido.