The Government has moved forward the legal process that means Sinn Féin's Barry McElduff is no longer an MP.
The move is part of the age-old formalities that give effect to the resignation of Members of Parliament.
A statement from HM Treasury said: "The Chancellor of the Exchequer has this day appointed Barry McElduff to be Steward and Bailiff of the Three Hundreds of Chiltern."
It comes as the fallout from his resignation over the Kingsmill video controversy continues to be felt in Northern Ireland.
West Tyrone is facing into a by-election later this year.
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Mr McElduff resigned on Monday - 10 days after posting a video of himself with a Kingsmill-branded loaf of bread on his head on the 42nd anniversary of the Kingsmill atrocity, when 10 Protestant workmen were shot dead.
The abstentionst MP, who had already been suspended by his party for three months, has insisted that he had not meant the video as a reference to the sectarian murders near south Armagh in 1976.
However, he acknowledged the post had caused "deep and unnecessary hurt" to the Kingsmill families.
In the last General Election, which took place last year, Sinn Féin held the West Tyrone seat with 51% of the vote.
There has been speculation that unionist parties could agree on a unity candidate, potentially from the victims sector, to contest the by-election.