If Lord Mereworth's claim is upheld, all legislation passed by upper house in last decade could be declared voidMinisters are facing a legal challenge from a hereditary peer that threatens to unravel the law that reformed the House of Lords 10 years ago.Lord Mereworth, who lost his seat in the upper house as a result of the House of Lords act in 1999, has served a legal paper, called a protocol letter, on Lord Mandelson in his capacity as lord president of the privy council, as well as on Black Rod, Sir Freddie Viggers, claiming that the law is defective. It is a precursor to mounting a judicial review in the high court.The challenge has angered House of Lords campaigners ...