Miss Holden, soon to star in a new ITV adaptation of Miss Marple, has made no secret of her desire to settle down with Hughes, talking of their happiness in interviews.
The couple met through friends several years ago, but only became close after her separation from Dennis.
They broke up briefly, blaming the pressure of living in the spotlight, but soon reunited.
Whispers that the couple are to marry have been circulating for several months.
Miss Holden did little to dispel such rumours by sporting a large diamond ring on the third finger of her left hand. But that turned out to be a prop from the Cutting It set.