Automatically Trigger a by-election if an MP defects to another political party

Background

Our democracy relies on voting for a political party based on their Manifesto within constituency seats. If an elected MP decides to defect to another party then the reason they were voted in becomes Null & Void

Additional details

I want any MP that leaves the current party they were elected to represent to automatically vacate that parliamentary seat and have to re-stand for their "new" party in that seat. We don't vote for personalities we vote for policies based on the party in question manifesto. If an MP moves party between elections they are going against the will of the voters in that constituency. I feel allowing MPs to freely jump ship with no due process or accountabilty makes a mockery of our democratic process