If an MP resigns and triggers a by-election, they should not be eligible to compete in that by-election unless they are standing for a different party. By-elections cost the public purse and other parties money. An MP in a safe seat can resign just to make a political point and be re-elected.

This is about preventing the abuse of the parliamentary system. An MP who has been elected has a duty to their constituents. If they genuinely need to resign, or they feel that they must change party and therefore want to give voters a chance to choose again, then that is fair enough. But they should not resign if they are intending to stand again for the same party.