Who decides what "serious" is
What Jack G said. Legislation.
But the strange thing about it is I don’t think his expulsion would include the removal of his title… seems to something to do with the Monarchy granting it. “ Peerages which are offered as a gift or an Honour.” So, difficult to remove the title (welcome to the15th century) Only means he would no longer be able to attend the House of Lords.
So he would technically still remain the High Baron of BS, or whatever was given in this sham of a democratic system. Unless he relinquished it. At least he would lose 300 Sovereigns a day, plus all those fat PD’s.