The actress received the Best Actress honour for her turn as John Lennon's mother in Nowhere Boy and she used her acceptance speech to thank McAvoy, who was in the audience.
She cooed, "I'd really like to be Mrs. McAvoy for a minute and say thank you for seriously having to live with a flame-haired broken-hearted banjo player for quite some time."
It's going to be an exciting year for the happy couple - the McAvoys are expecting their first child together.
Also among the winners at the London Film Museum event, Fish Tank claimed the night's Best Film prize and Lord of The Rings star Andy Serkis was named Best Actor for his portrayal of disabled punk icon Ian Dury in Sex & Drugs & Rock & Roll.
Serkis dedicated the award to the late Blockheads rocker: "Ian, wherever you are, this is for you."
Monty Python star Terry Gilliam was also on hand to present Sacha Baron Cohen with the Peter Sellers Award for Bruno, while veteran director Nicolas Roeg won a special award for his contribution to film.