Lily, 28, who played flighty Lady Rose in the ITV1 show, revealed that discussions to bring it to cinemas were “definitely” under way.
Speaking at the Los Angeles premiere of her new film, Baby Driver, Lily said: “There’s definitely rumours and discussions going on.”
When pressed if she was involved in those discussions, she smiled and replied: “Um, maybe.”
The saga of the aristocratic Crawley family and their servants ended on Christmas Day 2015 after six seasons.
The finale delighted fans with happy endings all round – even for Lady Edith (Laura Carmichael), the most beleaguered of all the show’s characters who endured being jilted by one fiance, the death of another who left her pregnant and the endless sniping of her elder sister Lady Mary (Michelle Dockery).
Edith ended up ahead of Mary in the social pecking order when she married a Marquess while Mary married a second-hand car dealer, albeit an upper crust one.
The downstairs staff were also blessed with Anna (Joanne Frogatt) and Bates (Brendan Coyle) welcoming a baby boy and tricky footman Thomas Barrow (Rob James-Collier) being saved from redundancy by being given the job of assistant butler to Carson (Jim Carter).
Creator Julian Fellowes never ruled out a big screen version.
On Tuesday in a web chat with fans he said he was awaiting the “green light” from a studio.
He wrote: “I know the cast are behind it and there’s a big audience out there.
“On most movies, unless it’s Spider-Man 6, you’re taking a punt. But it’s pretty likely the Downton movie will happen.”
But though most cast members have been enthusiastic about the prospect of reuniting on the big screen, fans could be in for a major disappointment because Dame Maggie Smith said that six series of the television show were quite enough and a film version would be “squeezing it dry”.
The veteran actress, who delighted viewers with her performance as the Dowager Countess, said that the “meandering” plotlines of the series would not translate to film
She said: “They talk about there being a film but who knows. I hope you might tell me if you do know.”
Lily, 28, stars as the love interest of a getaway driver in Shaun Of The Dead director Edgar Wright’s latest film.
Kevin Spacey, Jon Hamm and Jamie Foxx also feature in the star-studded line-up.