The Treason Act 1423 (2 Hen.6 c.17) was an Act of the Parliament of England. It made it high treason for a person who had been indicted for treason to escape from prison (whether they were guilty of the original allegation of treason or not). This form of treason was abolished by the Treason Act 1547, although the Act was formally repealed in 1863.
References
Treason Act 1423 Wikipedia(Text) CC BY-SA