The amendments to China's Criminal Procedure Law, passed by the National People's Congress yesterday, represent one of the best pieces of legislation enacted by Beijing. If fully implemented, they will revolutionise the administration of justice. The 30-day limit on detentions for investigation should make it illegal to repeat past abuses, such as the holding of dissident Wei Jingsheng for 20 months without trial. They also ban the present practice whereby prosecutors can convict and pass sentence, without even bothering to bring suspects before a court. In future, all defendants should also be allowed early access to legal advice. If properly put into practice, such changes will bring China much closer to recognising the fundamental principle that everyone must be presumed innocent until proved otherwise. Unfortunately a question mark already hangs over how faithfully the new rules will be enforced. Senior public security officials have hinted that they will only implement them as they see fit. Yet such fine-sounding amendments will be of little use unless they are put into practice. As Beijing officials freely admit, they often have great difficulty ensuring national laws are respected by cadres in some of the far-flung regions of China. If national public security officials are unwilling to give the new rules their whole-hearted support, there is even less chance of them being respected in such areas. These amendments may be an extremely welcome step towards building a fairer and more modern legal system on the mainland. But any final judgment as to how much of an improvement they will make in practice must wait until it is clear whether they will be faithfully implemented.