TV executives are considering several character options for the catwalk queen who will follow in the footsteps of previous guest stars Kylie Minogue and comedy veteran Bernard Cribbins.
A bbc source revealed: "Doctor Who remains the Beeb's jewel in the crown and bosses love pulling out the stops to land a bigname star to add a bit of extra showbiz sparkle to the Christmas special.
"Agyness is the perfect choice. She's talented and fast becoming a household name."
The part will be the first big acting role for Agyness, who is best known as the face of designer brands like Burberry and Armani.
Agyness, 25 - real name Laura Hollins - was discovered while working in a chip shop in Ramsbottom, Lancs, in 1999. Since then she has won a string of lucrative contracts as well as carving out a career in music - lending her voice to indie band The Five O'Clock Heroes' single Who.
She now divides her time between London and New York after splitting from long-term boyfriend Josh Hubbard, lead singer with The Paddingtons, last month.
Two years ago, Dr Who bosses brought in comedienne Catherine Tate to play bride Donna Noble in festive special The Runaway Bride. She proved a hit with viewers and was brought back as the Doctor's assistant, replacing Freema Agyeman. Pop princess Kylie Minogue was drafted in last year to play waitress Astrid Peth in Titanic-themed episode The Voyage Of The Damned.
Doctor Who - currently starring David Tennant - was an instant ratings winner for BBC1 when it was revived in 2005 with Christopher Eccleston as the Doctor and former pop singer Billie Piper as his assistant.