UPDATE 1-Robbie Williams "proposal" was a joke-spokesman

(Adds spokesman, changes dateline, pvs SYDNEY)

LONDON Nov 27 (Reuters Life!) - British singer Robbie Williams "proposed" to his actress girlfriend, Ayda Field, live on Australian radio on Friday, but his spokesman later said it was a joke.

Field was in the studio with Williams, 35, for the "Kyle and Jackie O" show on Australian radio station 2DayFM in Sydney to promote his new album "Reality Killed the Video Star."

Presenter Jackie Henderson was telling him that Sydney has a bit of a reputation for proposals with celebrities at which point Williams turned to Field and said: "Is there anyone you want to get married to?"

She replied: "This is so awkward."

To which Williams said: "Will you marry me?"

After a pause, Field, 30, answered: "Yes, I'll marry you."

When asked whether Williams was serious, his London-based spokesman said: "He did say it, but in a jocular manner. They are not engaged."

One of Europe's most successful entertainers, Williams rose to fame as a member of the hit boy band Take That before forging a successful solo career.

The singer, who now lives in Los Angeles, has been out of the public eye in the last few years since he left a U.S. rehabilitation centre in March 2007 where he was treated for prescription drug addiction.

His new album is his first release in three years. (Reporting by Mike Collett-White and Belinda Goldsmith, editing by Paul Casciato) ((belinda.goldsmith@reuters.com; Reuters Messaging: belinda.goldsmith.reuters.com@reuters.net, +61 2 9373 1800))