Two Milan clubs, Hollywood and The Club, allegedly allowed rich clients to enjoy sexual favours from escorts while taking drugs.

In court documents released this week, a French escort said she saw numerous models and stars taking cocaine at the nightclubs, including former showgirl Canalis.

"I used cocaine along with other people, among whom was Elisabetta Canalis," Karima Menad said.

The evidence was part of an investigation which saw five people arrested earlier this week and both clubs closed down.

Miss Menad's testimony goes back to 2008, a year before 31-year-old Canalis began dating Clooney, 49.

There has been mounting speculation in the Italian press that Clooney, one of the world's most eligible bachelors, is about to ask Canalis to marry him.

The chief prosecutor in the investigation said the high-class prostitutes were paid in money and drugs to encourage clients to buy expensive alcohol.

"We're talking about girls of various nationalities, who operated as PR for the clubs - the so-called 'image girls', joining clients at private tables, inducing them to drink alcohol in order to increase the bill and offering sexual services at locations away from the club," said Frank Di Maio.

The most favoured and high-spending clients were allegedly given free cocaine, and then spent more money paying for sex with the call girls.

The nightclubs were regarded by VIPs as a sort of "free zone" where they were immune from the law and at liberty to do what they liked "far from the gaze of public opinion" as long as they had enough money, Mr Di Maio said.