Devilling

Devilling is the period of training, pupillage or junior work undertaken by a person wishing to become an advocate in one of the legal systems of the United Kingdom or Ireland.
Scotland.
The prospective advocate is placed under the care of a devilmaster, who traditionally must not be a Queen's Counsel. The pupil follows a programme of training as laid down by the Faculty of Advocates.
The process has an ancient heritage, as it is the legal right of the Faculty of Advocates to admit persons as advocates to the Courts of Scotland. This right was apparently granted by the College of Justice.
Ireland.
Devilling is a period of training undertaken by barristers in Ireland where they work under a more senior barrister (one who has been called for seven or more years but who is not a senior counsel) who is called their master. A barrister is called to the bar after successfully completing the course of barrister-at-law in the King's Inns, but during their first year of practice, they must devil for one year. It is common for barristers to also devil during their second year of practice. The work is generally unpaid and there is no obligation on the master to cover the costs of the devil. A barrister who has not devilled may still be recognised as fully qualified by the bar associations of other EEA member states, and practise in those member states in accordance with the relevant European Union (EU) directives.
England and Wales.
The term is used in the English legal system to refer to a junior barrister undertaking paid written work on behalf of a more senior barrister. The instructing solicitor is not informed of the arrangement and the junior barrister is paid by the senior barrister out of his own fee as a private arrangement between the two. This is one of the exceptions to the usual prohibition on fee sharing under the Code of Conduct for Barristers in England and Wales.
Treasury Devil.
The "Treasury Devil" is the colloquial term for the First Junior Treasury Counsel (Common Law), a private practitioner barrister who represents Her Majesty's Government in the civil courts, instructed by the Treasury Solicitor. It was a tradition that the Treasury Devil was made a High Court Judge after the end of his term in office. There is no current Treasury Devil. James Eadie QC, who was appointed in 2009 when he was already a QC, holds the position of First Treasury Counsel (Common Law).
Treasury Counsel (Common Law) should not be confused with the criminal barristers appointed to the Treasury Counsel team who are responsible for prosecuting the most serious criminal cases. The team is headed by the "First Senior Treasury Counsel (Criminal)" and is composed of ten senior and seven junior Treasury Counsel. Treasury Counsel (Criminal) are so-named because historically they were also instructed by the Treasury Solicitor (who in earlier times was also Director of Public Prosecutions), although criminal prosecution is now overseen by the independent Crown Prosecution Service.