Parliament will debate a petition calling for by-elections to be automatically triggered when MPs defect to another party after it passed the 100,000-signature threshold, as the Government reiterated it has “no plans” to change current arrangements.

The petition, hosted on the UK Government and Parliament website, had reached 127,396 signatures on Thursday evening. An update on the petition states: “Parliament will debate this petition on 16 March 2026,” with viewers able to watch proceedings online via Parliament’s YouTube channel.

The campaign argues that voters should be given the chance to decide whether they still want to be represented by an MP who changes party, saying constituents should be able to “agree or not with their elected official” after a defection.

Under current practice, MPs who switch parties can keep their Commons seat for the remainder of the Parliament. They may continue to sit as a member of their new party or as an independent, and can choose to stand down to trigger a by-election, but are not required to do so.

In a written response published on Monday, 9 February, the Government said it would not be changing the rules, citing what it described as an established constitutional principle.

“There are no plans to make changes to the current constitutional arrangements, whereby voters elect individual candidates, and not the political party they represent,” the statement said. “It is an established constitutional principle that at UK General Elections, voters cast their vote for individual candidates, and not the political party they represent.”

A Cabinet Office spokesperson added that the decision to remain in Parliament or resign rests with the MP. “When a Member of Parliament (MP) decides to change their party affiliation, it is for the MP to decide whether to continue to sit in the House of Commons (as a representative of their new political party or as an independent MP) or to stand down from their seat to trigger a by-election and, if they wish, seek re-election,” the spokesperson said. “There are no plans to make changes to the current arrangements.”

The petition was created by Barry McIlhinney, who wrote that voters choose both the individual candidate and the party’s overall direction and policies. “Regardless of political views I believe you vote for both the individual candidates and their stance on issues and the more general direction and policies of the party they stand for,” he said in the petition text.

“When an MP decides that they no longer wish to be a member of the party they stood for when you voted for them the electorate should have the opportunity to also change their mind by voting in a by-election,” he added.

The renewed focus on defections follows a series of high-profile moves from the Conservative Party to Reform UK in recent weeks.

Andrew Rosindell was cited as one of the Conservative MPs to switch to Reform, following Robert Jenrick, who joined the party after being sacked by Conservative leader Kemi Badenoch. Suella Braverman announced her defection to Reform UK on 26 January.

The departures have increased the number of sitting MPs in Nigel Farage’s party to eight, adding to scrutiny of whether a Commons seat is best understood as belonging to an individual representative or as a mandate for a party platform.

While a parliamentary debate does not in itself change the law, reaching the threshold means the issue will be aired formally in Parliament, with campaigners expected to use the debate to press for reform and ministers set to defend the current position.

The Government’s response makes clear that it regards the existing system as rooted in the principle of individual representation, rather than party ownership of seats. Campaigners backing the petition argue the practical reality of modern elections is that party affiliation is central to how many people vote, and that a change in party should require renewed approval from constituents.

The petition remains open for signatures ahead of the scheduled debate on 16 March.