What are the legal aspects of 'packing' the Lords with Brexit-friendly peers?

The recent string of government defeats in the House of Lords over amendments to the European Union (Withdrawal) Bill has reignited the debate over the role of the Lords in a modern democracy. The Daily Mail published a characteristically trenchant headline suggesting that we should "pull the plug" on the "traitors in ermine". With 12 new peers just announced - nine of whom are Conservative – Francis Young considers the legal aspects of ‘packing’ the Lords with pro-Brexit members.