The former Corrie actress will star alongside Ncuti Gatwa and Jonathan Groff in the forthcoming run of the cult BBC sci-fi series, which turns 60 this year.
But insiders say that while Millie has thrown herself into the project, she has been struggling to deal with night shoots since filming began in Cardiff last month.
They also claim the actress’ attitude has not gone down well with members of the production team.
One said of Millie, who plays new companion Ruby Sunday: “No one could question Millie’s commitment to Doctor Who, but there is a lot of pressure coming into a role like this.
“She is determined to get it right. But the days are long and at times, when night filming has been suggested, she has made her feelings clear.
“Millie is a pro on set and although night shoots are part of the job, they can be tiring for even the most experienced actors.
“She won’t be the first or last person to be a bit annoyed by a night shoot, but it has won her some snippy comments behind the scenes. The word ‘diva’ has been used once or twice when tempers are fraying.
“Everyone on set wants the show to be as good as it can be within the time frame they have, and that does take its toll on people at times.”
Millie, who played Kelly Neelan in Coronation Street, quit the soap last year.
Her new Doctor Who co-star Ncuti will become the 15th Doctor in the upcoming series of the hit sci-fi show, due to
air next year.
With all the effort going into filming, we’re sure the finished result will be pretty epic.