Also, in answer to OG, when you say, "[the]Implementation period should be as short as possible...", that period is when the UK will finally start to negotiate a new trading relationship with the EU. Past experience should tell you that 14 months is impossibly short to succeed in negotiating anything of that scope, whether or not intentions on both sides are good. Trade Deals always take longer. Therefore there will have to be an extension if the government wishes to reach a deal; and, if there is no extension, then it turns out that "No Deal" occurs instead at the end of 2020. Parliament is entitled to at least try to debate if it wants the question of an extension to be at the discretion of government.