The star is being presented with the award by the Duke of Cambridge at the event at London’s Royal Opera House in Covent Garden.
Dame Helen – who has played the monarch on stage and screen, and won the leading actress Oscar in 2007 for The Queen – joins other winners of the prestigious award including Martin Scorsese and Sir Christopher Lee.
“I’ll try not to be too emotional about it,” she said. “The emotional quotient, if my lip starts trembling, is the thought that my parents aren’t here to be proud and that’s the trouble with getting these sort of lifetime things because they do tend to come towards the latter part of your life as opposed to the beginning, and they would have been so proud and so pleased for me.
“They would be so relieved that it all worked out”.
But the actress said she was not “proud” of her own career, saying: “I look at everything and think ‘God you weren’t very good in that were you really, Helen?’”
Asked if she had any regrets over a career spanning almost 50 years, the 68-year-old said: “You can never think that, even with the major disasters you can never think that, because everything you learn on.”
Tonight’s event is hosted by Stephen Fry with guests including Leonardo DiCaprio, Uma Thurman and Tom Hanks.
It is widely seen as a dry run for next month’s Oscars, and Steve McQueen’s 12 Years A Slave is tipped to continue its award-season success.
The film, which stars Chiwetel Ejiofor as a free man kidnapped and sold into slavery in America’s deep south, has ten nominations including for best film and best director.
Ejiofor is nominated for the leading actor award while co-stars Lupita Nyong’o and Michael Fassbender are nominated for supporting actress and actor.
Ejiofor faces competition for the leading actor award from veteran Bruce Dern for his role in Nebraska and Hollywood stars Christian Bale, DiCaprio and Hanks.
The other contenders for best film are Philomena, Captain Phillips, American Hustle and Gravity.
Philomena also gets Dame Judi Dench a nomination for the leading actress award.
She is in the running with American Hustle’s Amy Adams, Cate Blanchett, Emma Thompson and Sandra Bullock for Gravity.
Gravity leads in number of nominations with 11.
The event, formally known as the EE British Academy Film Awards, is broadcast on BBC1.
Best film 12 Years A Slave; American Hustle; Captain Phillips; Gravity; Philomena
Best actor Bruce Dern, Nebraska; Chiwetel Ejiofor, 12 Years A Slave; Christian Bale, American Hustle; Leonardo DiCaprio, Wolf Of Wall Street; Tom Hanks, Captain Phillips.
Best actress Amy Adams, American Hustle; Cate Blanchett, Blue Jasmine; Emma Thompson, Saving Mr Banks; Judi Dench, Philomena; Sandra Bullock, Gravity.
Best director Steve McQueen,
12 Years A Slave; David O Russell, American Hustle; Paul Greengrass, Captain Phillips; Alfonso Cuaron, Gravity; Martin Scorsese, Wolf Of Wall Street