MPs will debate changing the law on holding by-elections if an MP switches allegiance following a series of defections from the Tories to Reform UK.

The petition, which surpassed 128,000 signatures, surged after Newark MP Robert Jenrick and Romford MP Andrew Rosindell crossed the floor to Nigel Farage’s party.

Almost 1,000 people signed the petition in Suella Braverman’s constituency of Fareham & Waterlooville, with just over 500 backing automatic by-elections in Danny Kruger’s seat of East Wiltshire.

The debate, which will be opened by Liberal Democrat MP Dr Roz Savage, will take place at 4.30pm on March 16.

Sir Keir Starmer’s Government is expected to send a minister to respond to Dr Savage.

The Cabinet Office 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.

“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.

“There are no plans to make changes to the current arrangements.”

Despite criticisms about Reform UK’s newest recruits, by-elections have rarely been held as a result of a defection throughout Britain’s political history.

The two most significant recent examples came in 2014, when Douglas Carswell and Mark Reckless held onto Clacton and Rochester & Strood after leaving the Tories for Ukip.

Other examples include William Allen Jowitt’s defection from the Liberals to Labour in 1929, Dick Taverne’s 1973 change from Labour to Democratic Labour and Bruce Douglas-Mann’s defeat in the 1982 Mitcham & Morden by-election.

There have been at least two recent attempts to change the law on holding by-elections as a result of a defection.

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Ex-Tory MP Chris Skidmore proposed requiring a by-election in 2011.

A similar private members’ bill was brought forward by Anthony Mangnall following a series of defections to Change UK and the Liberal Democrats during the Brexit years.

However, Reform UK is not the only political party to recently benefit from defections.

Labour welcomed a number of Tories into its ranks ahead of the 2024 General Election, including Christian Wakeford, Dan Poulter and Natalie Elphicke.

Meanwhile, Paul Marsden switched from Labour to the Liberal Democrats during Tony Blair’s stint as Prime Minister.

Alan Howarth made history with his defection in 1995, later becoming the only politician since 1979 to serve as a Government Minister for two different parties.

Ex-Basingstoke MP Andrew Hunter raised eyebrows in 2004 when he opted to defect to the Northern Irish Democratic Unionist Party.

However, following Lee Anderson’s switch to Reform UK ahead of the 2024 General Election, Mr Farage has decided not to hold by-elections for his switchers.

An Ipsos poll conducted in 2024 suggested a plurality of Britons would support holding a by-election if an MP switches allegiance.

Almost half – 49 per cent – of respondents backed holding a by-election.

Meanwhile, 23 per cent claimed Mr Anderson’s defection was close enough to the upcoming general election not to require a snap poll.

Reform UK is hoping more Tory MPs will defect to Reform ahead of the 2026 Local Elections, with Mr Farage giving potential switchers just 83 days to make the move.