Why are there no additional jurors?

[osprey]

I have often wondered why we do not have additional jurors sitting on a jury. I know only 12 can judge a case but surley there have been many instances where a trial has had to be cancelled when a juror fell ill and the case had to start again. Why can't there be some alternate jurors (as in America) who are able to take the place of one of the original 12 if one has to leave for whatever reason and then, when it is time for the jury to deliberate, any alternate jurors are dismissed and the 12 jurors can decide the case without any need for a case to start again?

[Tichfield]

In England and Wales a crown court trial can continue so long as there are 9 jurors left to consider a verdict.

http://en.wikipedia.org/wiki/Jury_%28England_a nd_Wales%29

[Stu Dent]

There are 15 jurors in Scottish courts. Sometimes a juror will become ill and the trial can proceed with 14 jurors. I think this happened quite recently in fact during the 'Templeton Woods' murder trial.

[tufty7]

I have been called for jury service twice, believe me some people on there should not be allowed to choose what baked beans they have never mind the future of the person in the dock ,