It is the one moment every man wants to get right -- and which London floor-fitter Lefkos Hajji could hardly have got more wrong.

The luckless 28 year-old's dreams of giving his sweetheart, Leanne, 26, the ultimate proposal have literally vanished into thin air.

Hajji, of Hackney, east London, had concealed a $12,000 engagement ring inside a helium balloon. The idea was that she would pop the balloon as he popped the question.