LONDON, March 14 (Reuters) - Unlucky London suitor Lefkos Hajji watched a small fortune and plans to ask for his beloved's hand in marriage vanish into thin air.

The 28 year-old floor-fitter lost a 6,000 pound ($12,000) engagement ring and possibly the affections of his girlfriend when the helium balloon in which he had concealed the ring was whipped from his hands by a gust of wind outside a shop.

"I just watched as it went further and further into the air," he told The Sun newspaper on Friday. "I felt like such a plonker. It cost a fortune and I knew my girlfriend would kill me."

Hajji, who had intended to get his 26 year-old girlfriend Leanne to pop the balloon to find the ring, spent two hours in his car giving chase without success.

"I thought I would give Leanne a pin so I could literally pop the question," he said. "But I had to tell her the story -- she went absolutely mad. Now she is refusing to speak to me until I get her a new ring."

He is hoping the ring will still turn up.

"It would be amazing if someone found it," he added.

(Reporting by Peter Apps. Editing by Andrew Hough and Paul Casciato)