The reference to the British system which was employed during colonial times is probably when this educational system knew its greatest renown. Those who emerged from British schools did display a certain precision in language and thought and an acquaintance with the liberal arts as well as sciences, and they were, indeed, broadly educated. But, England today is hardly the same as that of the Victorian Age and somewhat later. Nevertheless, such institutions as Eton and Oxford yet retain great reputations.
It depends, perhaps, on how you measure the best. If we measure the effectiveness or quality of a system by its ability to prepare the broadest number of students for the world they will be entering, most of the information I'm familiar with, including a great deal of anecdotal accounts from friends, suggests that the British educational system suffers from many of the same problems that the American system does. If were are talking about the ability to train a small cadre of intellectual elites for academic and research pursuits, then the British system is probably among the world's best.
This question assumes too much, that is, it is not a fact that the British school system is the best in the world. It is certainly good, but to say that it is the best is another story. The schools in the United States, such as Harvard, Yale, Princeton, Stanford and the like are just as good, if not better. Also there are many more schools in the United States. That said, one of the reasons why the British school system is good is due to longevity. In other words, they have been in the education business for a long time.
The British do have an excellent system of higher education, but I don't know what criteria would be used to label them "the best". Since many of their schools have been in existence for a very long time and therefore have a history and tradition, we tend to think of them as excellent without truly evaluating them.
Harvard and Yale, for example, are often thought to be the best of the best, and they are surely fine schools. I don't know if they produce better graduates than MIT or Stanford though. They just happen to be the oldest colleges in the US, so they have elite status almost automatically.
I suspect we are all also operating under the influence of living, learning, and thinking from a Western European heritage and point of view. If we were to suggest to someone from an Islamic background that the British educational system is superior to the learning protected by the traditions of Islam, I am guessing they would disagree. If we made the same suggestion to the Chinese, Japanese, or Indians on the subcontinent, they would also quite possibly take issue with the assumption presented.
Britain has a long tradition of providing strong university-level educational experiences. I don't agree that makes it the "best in the world."
I don't think we can safely say that the British system is the best and most famous in the world. If it is, however, it is because of what the previous post said. It is because the British Empire was the largest and most powerful for a long time. This means that British educational institutions were long associated with the prestige of the empire.
I am currently studying the Finnish education system, that is currently being hailed as the best in the world. With that being said, I think much of the perception of the quality of British education reflects back to colonial days. Here in America, and in much of the world, our history is tied to Great Britain. Like #3 above, I am not an expert on their system; however, I believe the perception of their educational prowess might be greater than its reality.
I've heard about the colleges mentioned in post #2, but I'm not familiar with anything else about the British educational system. I know only too intimately of the problems with education in the American system. However, to be honest, I have not heard that the British have an exceptionally good system. I'm not saying they don't, I just haven't heard about it.
The British, or more appropriately English, educational system has a worldwide reputation for being among the best in the world. In particular, the colleges located in Oxford and Cambridge (which are actually both comprised of a number of separate colleges) are well known and very prestigious. Cambridge and Oxford have been hihgly respected universities for hundreds of years, and so being two of the longest-running schools in the world lends credence to their reputation for prestige. Admissions are highly competitive, and students who attend prestigious secondary schools (such as Eton) prepare for entrance to either Oxford or Cambridge as a way to continue an education of high social standing. Although other schools in Great Britain are considered excellent (such as Bristol, or the London School of Economics), Oxford and Cambridge still maintain the top reputation. The basic format of instruction is made up of tutorials, with small numbers of students engaging in discussion of required texts and assignments with professors: a system alwing for a very intensive and compreensive educational experience.