Mountford has teamed up with her former Apprentice sidekick Nick Hewer to tackle the issue of immigration in a two-part documentary for BBC1.
In 1978, Margaret Thatcher was famously criticised for declaring that British people feared being "swamped" by immigration.
Now Mountford has told Radio Times magazine: "I think the question is how we deal with immigrants here, not whether we stop them coming.
"We've allowed ghettos to grow up and - to use Thatcher's word - areas to be swamped by people of one ethnic origin."
Asked whether immigration was just about economics, she replied: "No, because of the cultural issues.
"If you live in a community that has been taken over by a different ethnic group, even if they bring prosperity and your high street is booming, I doubt you'd think, 'Gosh, aren't we lucky we're doing well out of this'. You'd think, 'I don't want to live here any more'."
Hewer told the magazine: "Ted and Margaret (a couple featured in the documentary) do feel they've been swamped and they've moved home as a result. Margaret calls it 'white flight'."
He added: "And you can't blame them for feeling that way. But 'swamping' only applies if there's no integration. If new people moving into an area, try to integrate, you're not swamped, are you?"
Nick And Margaret: Too Many Immigrants? pairs up people who are opposed to immigration with immigrants to see how they live and work.
To be screened this summer, the two-part series looks at the issues of jobs, housing and what it means to be British.