Speaking to the Mail on Sunday’s You magazine, she said that being a pupil at Beverley High School in East Yorkshire while working on film sets was very difficult.
She said: “I was accused of being too posh because during stints away from home any trace of a Yorkshire accent would fade away.
“The bullying would take the weirdest forms.
“For example, people would come up to me and shout the name of the project I happened to have been working on and then just walk away.
“It is incredible how horrible girls can be.
“It was psychological warfare and it was really hard to cope with.”
Tomlinson added that her past experiences helped her to play the character Demelza.
“I do think that she has a fear of not fitting in, which I can sympathise with,” she said.
The new period drama of Poldark sees Tomlinson in “passionate” love scenes with Captain Ross Poldark, played by Aidan Turner.
Talking about hard it is for her boyfriend to watch, she said: “It must be especially difficult when your co-star is someone like Aidan, who looks like a god among men.
“But my boyfriend, bless him, does really well.
“He is a really calm person, whereas I can be a complete nutcase at times.
“If it was the other way round, I would be psychotic about it.”
The show’s pilot episode last weekend attracted a viewing audience of more than 7 million people.
Based on a series of historical novels by Winston Graham, it was a hit television show in the mid 1970s before this latest incarnation hit the screens.