MPs that defect to another party should trigger an immediate by-election

Background

Change the rules so that when a sitting MP defects to a different party, a by-election is immediately triggered

Additional details

so that the electorate of the relevant constituency get a chance to be represented in parliament by an MP that represents them and the manifesto the majority initially voted for. The votes should not follow the MP, as by definition of defection, the MP no longer represents the voters that put the MP in parliament, and the only way to check this is to have a by-election