The BBC Television series "Garrow's Law" is proving to be very popular. It is based on criminal trials which took place at The Old Bailey in the 18th century and highlights both the harshness of the system and the unfairness of the trial processes of the day. The Old Bailey Online website makes available a fully searchable, digitised collection of all surviving editions of the Old Bailey Proceedings from 1674 to 1913, and of the Ordinary of Newgate's Accounts between 1676 and 1772. It allows access to over 197,000 trials and biographical details of approximately 2,500 men and women executed at Tyburn, free of charge for non-commercial use.
Even in modern times, miscarriages of justice are possible. However, great care is taken in the process of deciding whether to prosecute and, if so, on what charges. Crown Court trials entail extensive examination of the evidence. The draconian sentences of yesteryear no longer exist. There is an appeal process and there is also the Criminal Cases Review Commission which was set up after the Royal Commission on Criminal Justice considered the aftermath of the Birmingham Six and certain other cases. Some progress has been made but the quest for justice must always continue and there is little doubt that the rules of evidence have been rebalanced in favour of the prosecution - e.g. admission of "bad character" evidence and a more permissive regime relating to hearsay evidence - Criminal Justice Act 2003.
Addendum 1st December 2010: For a view that the Criminal Cases Review Commission is a failure - see The Guardian 1st December 2010. The article is by journalist Bob Woffinden who has written extensively on miscarriages of justice. He criticises the "success" statistics claimed by the CCRC. He condemns them as "characterised by puisllanimity and procrastination."