If Brexit has not be completed on October 31st, then a general election has to be held before the end of the year even if the opposition parties do not want one. Through an election, the British public will make it clear to all of the current serving MP's that Brexit has to be completed.
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The British public is fed up with how the majority of Parliament is acting on their own interest and benefit, and not of that what was voted on by the British public. Members of Parliament have to remember, that it is the British public, their constituents, are who put them into their positions in Parliament and that they can be removed from that position if they do not carry out and replaced with new MP's who will carry out the duty of what has been voted on by the British people.