When a Member of Parliament decides to leave the party for which they were elected, it is for them to decide whether to stand down from their seat in the House of Commons and seek re-election in the subsequent by-election, or to continue to sit in the House of Commons as either an independent or by joining another political party.

There is no requirement for a Member of Parliament to stand down and cause a by-election to be held if they decide to leave the party for which they stood and were elected to join another political party. This is because the formal position at UK Parliamentary elections is that electors cast their vote for individual candidates, not the political party they represent; although it is recognised that many people vote on the basis of party preference.

It is generally agreed that a candidate, if elected to the House of Commons, is not deemed to be a delegate of a particular party, and will hold the office to which they have been elected in a personal capacity.

A Member of Parliament who decides to leave the party for which they were elected and to continue to sit in the House of Commons will be required to stand as a candidate at the next General Election if they wish to remain in office.

Amending the existing law would involve a significant change to our constitutional arrangements, and would raise important issues about the role and status of Members of Parliament, which would need careful consideration. We currently have no plans to do this.

Cabinet Office.