The businesswoman said she would “absolutely” take legal action if she felt Theresa May and her Brexit ministers were not doing their “duty”.
Speaking at Advertising Week Europe, as part of a debate titled ‘Is Westminster the New Brussels?’, Ms Miller accused high-ranking Brexiteers of attempting a “power grab”.
She said MPs were in danger of being overlooked by Theresa May and Parliament's sovereignty ignored.
Ms Miller previously took the Government to court over its refusal to grant MPs votes on various aspects of the Brexit process.
While she succeeded in forcing Mrs May into allowing MPs to vote on a number of proposed amendments to the Brexit Bill, the Government nonetheless got through the process unscathed by any forced changes.
But now Ms Miller said she will once again take the Government to court if she feels Parliament is being overruled by Mrs May’s cabinet.
READ MORE: What is the Brexit plan?
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Gina Miller has threatened to take the Government to court over Brexit
She said: “I will uphold the ruling in my case which is: only Parliament is sovereign when it comes to diminishing or taking away people’s rights.
“We have numerous acts which need to be passed and if the Government try to bypass them or bring in a resolution I will take them back to court.”
She said she was concerned by the “diminishing” role MPs were playing in the Brexit process and accused Parliament of “voting against itself” during the raft of proposed amendments.
ADVERTISING WEEK EUROPE
Ms Miller was speaking in a debate called ‘Is Westminster the New Brussels?’
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Ms Miller said: “We are now going into Brexit where I see power will reside with a few in Westminster, and they will override Parliament.
“I’m particularly worried about the process over the next 18 months or two years actually diminishing parliamentary sovereignty and MPs’ powers, and it very much sitting with the executive and the Prime Minister.
“It will be the executive, literally a handful of ministers and the Prime Minister, who will decide on our futures and decide which rights we keep and which laws we keep.”
Gina Miller succeeded in securing more power for MPs during the Brexit process
Ms Miller also said, despite her protestations about the Brexit process, she was against a second referendum on whether Britain leaves the bloc.
She said: “I have to say I am not in favour of a referendum.”
She joked she had “managed to upset both sides” during her court battle.
Theresa May has been repeatedly frustrated by Ms Miller's legal actions
Ms Miller said: “I refused to be drawn into the binary remain or leave.”
She did say, however, she did not believe “this is the right time to be leaving”.