European Union (Withdrawal) Bill

My Lords, the noble Lord, Lord Newby, has offered a tutorial in the constitution. I am a relatively new Member of this House—some people have been here far too long, I agree—but I understood that something called the Salisbury convention meant that the opposition parties would agree with those things put forward in the manifesto of a governing party. Perhaps somebody could explain to me why, when the Conservative manifesto said that we would leave the customs union, opposition parties—and, I regret to say, some of my noble friends—have determined that we shall not. Surely if it is in the manifesto, it has been agreed by the people of this country and we should accept the Salisbury convention. Perhaps at some point the noble Lord, Lord Newby, or the noble Baroness, Lady Smith, might explain what happened to the Salisbury convention and why it is being ignored left, right and centre.