The Junkhearts and The Hour actress said that Glorious 39 director Stephen Poliakoff was "very generous" when he told Digital Spy that she was "the next Kate Winslet" back in 2009.
Garai told Stylist of Poliakoff: "He's a very dear friend of mine, who I love. He's an incredibly kind director and an amazingly brilliant man.
"He was obviously trying to garner as much publicity for the film as possible. And that is a good way to get publicity! Obviously, I'm flattered. It's a very nice thing to say - albeit untrue."
When it was suggested that her and Winslet's career paths have been similar, she added: "Have they? I think she'd done Titanic by the time she was 23.
"She was the biggest movie star in the world. Apart from that our careers are exactly the same!"
In March, Garai was linked to a new ITV programme about the sinking of the Titanic, which will be penned by Downton Abbey writer Julian Fellowes.
The actress recently confirmed details of series two of The Hour.
> The Hour: Dominic West, Romola Garai interview
Watch our Glorious 39 interview with Romola Garai below: