A bill, act or writ of attainder was a piece of legislation that declared a person or persons guilty of a crime. A bill of attainder allowed for the guilty party to be punished without a trial. A bill of attainder was part of English common law. Whereas Habeus Corpus guaranteed a fair trial by jury, a bill of attainder bypassed this. Despite the unfair nature of a bill of attainder, they were only abolished in the United Kingdom in 1870.
The word “attainder” meant tainted. A bill of attainder was mostly used for treason - as in the cases of Laud and Strafford - and such a move suspended a person's civil rights and guaranteed that the person would be found guilty of the crimes stated in the bill as long as the Royal Assent was gained. For serious crimes such as treason, the result was invariably execution. The guilty person's family would find that his/her property was confiscated by the Crown as he/she had no right to make a will. All titles held would go to the Crown. In this sense, the attainted person's family was also held to be guilty as they were also punished, though not to the same degree.
A bill of attainder was a convenient method used the the Crown to remove nobles who were deemed to be getting above themselves - though attainders were rarely used and probably the most famous cases of them being used involved Parliament and Archbishop Laud and the Earl of Strafford. Though the source of the bills may have been different, the results were the same.
The first bill of attainder was used in 1321 and the last was in 1798. The most famous people to be executed as a result of a bill were Thomas Cromwell in 1540, Catherine Howard in 1542 and Laud and Strafford in 1641. In Catherine's case, Henry VIII delegated the passing of the Royal Assent to others so that he did not have to sign the document himself.
In May 1660, certain regicides were also served with bills of attainder even though they were dead - Oliver Cromwell and John Bradshaw (the judge at Charles I trial) were the most famous. The bills served on them were backdated to January 1649 - the month and year Charles was executed. The bill stated that all the bodies were to be dug up and symbolically executed as befitted traitors.