MPs who change party allegiance

On 15 September 2025 Danny Kruger defected to Reform from the Conservative Party. Only a small number of cases see an MP leave one party for another, in most cases an MP leaves their party to sit as an independent.

How do MPs change political parties?

MPs are allowed to change their party affiliation at any time. This is often referred to as "crossing the floor", because the MP will usually change from sitting on the government benches to the opposition benches or vice versa. This is allowed because individual MPs, rather than parties, are elected to the House of Commons, so even if the member changes their party, they remain the chosen representative of their constituency. 

Why do MPs change allegiance?

There are a range of reasons why MPs change their affiliation in the House of Commons. They could feel their views are better represented by another party, by defecting to a new political party, or joining another party after being suspended from their original party. They may also choose to sit as an independent MP and may choose to do this before deciding to join another party. In the last parliament, there were many MPs who defected including Natalie Elphicke who defected from the Conservative Party to Labour in May 2024. Danny Kruger is the first sitting Conservative MP to defect. In July, Zarah Sultana left the Labour party, announcing she would set up a new party with Jeremy Corbyn.

MPs can also change their party affiliation if they have the whip removed or are suspended from the party. This is when the chief whip of a party or the party leadership chooses to expel a member. In these cases, the member can choose to continue as an independent MP. In July 2025, four Labour MPs had the whip removed and now sit as independent MPs. MPs who have had the whip removed can choose to join another party if the whips or leadership from that party are willing to accept them. For example Lee Anderson, who was suspended from the Conservative Party in the last parliament, now sits as a Reform MP after a period as an independent MP.

Most MPs who change party allegiance leave their party to sit as an independent MP. 

How often do MPs change allegiance?

Between 1979 and 2024, there were 202 cases where MPs have changed allegiance. Just over half (56%) had the whip removed or were suspended, and  43% resigned from their party. Two MPs Charles Kennedy and Robert Maclennan are recorded as N/A as they left the SDP to join the newly formed Liberal Democrats in 1988. 

The 2017-2019 parliament had a high number of changes in party allegiance. In total 18 MPs resigned and 33 had the whip withdrawn (some moved more than once resulting in 59 changes in total). These figures reflect the unrest of the post-Brexit years in the House of Commons. In February 2019, eight Labour and three Conservative MPs defected in response to their parties’ stance on Brexit. They later set up Change UK. On 3 September 2019, 21 Conservative MPs had the whip withdrawn when they voted against the government and backed a motion in favour of legislation to delay the date the UK formally exited the EU. 

In the last parliamentary term, a total of 39 MPs have left, or been removed from, their party in the current parliamentary term, including high-profile defections from the governing Conservative Party. Despite this, it is still unusual for an MP from the party in government to defect to an opposition party. Before April 2024 the most recent examples were Christian Wakeford, the MP for Bury South, who switched from Conservative to Labour – the official opposition –  in 2022 and Philip Lee who left the Conservatives to join the Liberal Democrats in September 2019, leaving the government with no working majority.

In 2014 both Mark Reckless and Douglas Carswell defected from the Conservatives to join UKIP. These were the first defections from the party of government to an opposition party since 2001, when Paul Marsden defected from the then Labour government to the Liberal Democrats.

Do MPs who leave their party face any sanctions?

There are no formal sanctions facing an MP who decides to leave their party. They may, however, face pressure from other MPs and the public. 

An MP who leaves their party can remain in their seat as there are no rules requiring them to stand down or face a by-election. The convention is that MPs are elected directly to represent their constituency and they can continue to do this as an independent or member of another party. However, some MPs have chosen to resign their seats to re-contest them in a by-election for their new party. This has not been done since 2014, when the two Conservative MPs, Douglas Carswell and Mark Reckless, switched their allegiance to UKIP and then successfully contested by-elections. 

There have been some attempts to change this rule in the past, although only through private members' bills. Both Chris Skidmore in 2011 and Anthony Mangnall in 2020 introduced private members' bills to require a by-election if an MP changed parties. However, neither of these bills made it to second reading and so were not passed. 

Many MPs who leave their party either stand down at the next election or find they are unsuccessful in retaining their seat. Others are more successful in extending their parliamentary career. Alan Howarth left the Conservatives to join Labour in 1995, and was re-elected as a Labour MP in 1997. He later earned the accolade of being the only person since 1979 to serve as a government minister for two different parties.