THERE are many differences between the American and the British political systems, despite the lip service that is frequently paid on both sides to the common commitment to the values first expressed in the Magna Carta. The difference most often commented on is the deliberate “separation of powers” in the American system so that the legislature, the Senate and the House of Representatives, and the executive, the White House, are complementary to each other rather than, as in Britain, one and the same. There is a further difference, perhaps the most important of all, which is the status and role of the US Supreme Court which plays an influential quasi-political role in interpreting and reviewing laws passed by the legislature. It is for this reason that President Bush's nomination yesterday of Judge John Roberts as US Chief Justice to succed William Rehnquist, who died at the weekend, is of more than passing interest to those of us outside the United States. If proof were needed of the political implications of Supreme Court judgments it is readily available in the decision of the Court to stop ballot recounts in Florida and, in effect, to hand the White House to George W Bush in the contentious Presidential election in 2000; Judge Rehnquist played a key role in this judgement. Under his 19-year leadership American judisprudence moved consistently to the right of the political spectrum, for instance in strengthening the rights of States over the Federal government, by supporting the role of religion in American public life and by limiting some defendents' rights. President Bush nominated Judge Roberts as one of the nine-member Supreme Court when Judge Sandra Day O'Connor retired in July and his confirmation hearings in the Senate were due to start this week; however, by naming him yesterday as Chief Justice, Mr Bush has simplified the confirmation process. Although this nomination is unusual, since Mr Roberts will leap-frog over the other long-serving members of the Supreme Court, he is respected as a judge with centre-right leanings. In other words, President Bush has resisted the temptation to appoint a more extreme right-wing candidate such as the controversial Judge Antonin Scalia who many Republicans would have liked to see as Chief Justice.