Allen Burry said the couple were "an item" - but added reports of an engagement party planned for 25 September had been confused with news of a joint birthday party planned for that day.

He said: "They took it another step and made more out of it than there really is."

But asked whether an engagement announcement was possible at that time, Burry said, "Well, September's a long way away."

Every year, Douglas has a party at his Florida mansion with people who share his birthday, including Barbara Walters and Christopher Reeve.

"Last year, when they found out Catherine also shared the birthday, they invited her to the party but she was filming and couldn't make it," Burry said.

"This year, she's going."

Zeta Jones will be 30 that day and Douglas will be 55.

Marrage speculation

The couple have been at the centre of intense tabloid speculation ever since they were first seen by photographers on a yacht off Majorca in June.

Distinguished heritage: Kirk Douglas

Last month Zeta Jones, whose latest film The Haunting has been a hit in the US, was seen wearing a £180,000 diamond and gold ring, leading to speculation they were engaged.

At the time she told celebrity magazine Hello! they shared "a very special relationship", adding: "He's a charming guy and a real gentleman. He's the kind of person it's easy to feel good with."

Michael Douglas, whose films include Fatal Attraction and Basic Insinct, divorced his wife Diandra in 1997 after 20 years of marriage.

The son of Kirk Douglas, he started his career as an assistant producer on his films in the 1960s. He first became known worldwide with Karl Malden starring in TV police drama The Streets of San Francisco in 1972.

He was executive producer of One Flew Over The Cuckoo's Nest in 1975, but it took until the mid 1980s and Romancing The Stone for his talents in front of the camera to be fully realised.

Respected in Hollywood

Respected for his easy-going demeanour off-screen, his private life has frequently been under the spotlight - leading to lurid tabloid reports that he was addicted to sex, which he denied.

He also works as a United Nations Messenger For Peace, and next year will appear in A Song For David - his first film with his father.

Catherine Zeta Jones: Tabloid favourite of the early 1990s

Meanwhile, Zeta Jones' rise to fame has astonished Hollywood.

She left the UK four years ago to seek her fortune in Hollywood, having become a household name in 1991 starring alongside David Jason and Pam Ferris in ITV drama The Darling Buds of May.

She also became a fixture in the tabloid press. Her former loves included former children's TV presenter John Leslie and actor Angus McFadden.

Her first big Hollywood hit came last year in The Mask Of Zorro, when her on-screen chemistry with Antonio Banderas made the film a huge hit in the US and the UK, and made her a success almost overnight.