A McKenzie friend assists a litigant in person in a court of law in England and Wales. This person does not need to be legally qualified. The crucial point is that litigants in person are entitled to have assistance, lay or professional, unless there are exceptional circumstances.
Their role was set out most clearly in the eponymous 1970 case McKenzie v McKenzie. Although in many cases a McKenzie friend may be an actual friend, it is often somebody with knowledge of the area, and the trend is heavily in favour of admitting McKenzie Friends. He or she may be liable for any misleading advice given to the litigant in person but is not covered by professional indemnity insurance.
McKenzie v. McKenzie was a divorce case in England. Levine McKenzie, who was petitioning for divorce, had been legally aided but the legal aid had been withdrawn before the case went to court. Unable to fund legal representation, McKenzie had broken off contact from his solicitors, Geoffrey Gordon & Co. However, one day before the hearing, Geoffrey Gordon & Co. sent the case to an Australian barrister in London, Ian Hanger, whose qualifications in law in Australia did not allow him to practice as a barrister in London. Hanger hoped to sit with his client to prompt him, take notes, and suggest questions in cross-examination, thereby providing what quiet assistance he could from the bar table to a man representing himself. The trial judge ordered Hanger not to take any active part in the case (except to advise McKenzie during adjournments) and to sit in the public gallery of the court. Hanger assumed his limited role was futile and did not return for the second day of the trial.
The case went against McKenzie, who then appealed to the Court of Appeal on the basis that he had been denied representation. On 12 June 1970, the Court of Appeal ruled that the judge's intervention had deprived McKenzie of assistance to which he was entitled, and ordered a retrial.
McKenzie friends in specific jurisdictions
In September 2006, the Subordinate Courts of Singapore started a pilot project called the Lay Assistant Scheme in which persons, usually with some legal knowledge, attend hearings with litigants who are not represented by lawyers to advise them on non-legal issues and help them with administrative tasks. The scheme, a modification of the U.K.'s McKenzie friend system, is intended to assist litigants who are not eligible for legal aid as they have an annual salary exceeding S$10,000 but cannot afford a lawyer. For the litigant to qualify, the other party must be legally represented.
Lay assistants are not allowed to act as lawyers and may not address the court; any breach of court rules may render them liable to a maximum fine of $1,000 or imprisonment of up to six months.
Plans for introducing McKenzie friends in court proceedings were first announced by Chief Justice Chan Sek Keong in May 2006. Students from the Pro Bono Group of the Faculty of Law, National University of Singapore, have been participating in the scheme.
England and Wales
In English courts, where a case is being heard in private, the use of a McKenzie friend has sometimes been contentious. This is a particular problem in family court hearings, where it has been held that the nature of the case is so confidential that no one other than the litigants and their professional legal representatives should be admitted to the court.
A 2005 Court of Appeal case, In the matter of the children of Mr O'Connell, Mr Whelan and Mr Watson, clarified the law in this area. The result of the appeal has legitimised the use of McKenzie friends in the family court and allowed the litigant to disclose confidential court papers to the McKenzie friend.
England and Wales allow fee charging McKenzie Friends, who may charge for their services, including the giving of legal advice. A recent report by the Legal Service Consumer Panel found that fee charging McKenzie Friends were a net benefit. The report stated, "They should be viewed as providing valuable support that improves access to justice in the large majority of cases" 
Scotland has a separate legal system to England and Wales and only started to permit McKenzie Friends in 2010. McKenzie Friends were permitted via legislation rather than via a court case. The one major difference between England and Scotland is that in Scotland McKenzie Friends are not permitted to receive remuneration.
-  P 33;  3 WLR 472;  3 All ER 1034, CA
- McKenzie Friends, Family Law Week, Retrieved 15 June 2015
- Forsyth, John (4 May 2009). "Little help from my friends". The Scotsman. Retrieved 23 September 2013.
- "Litigant In Person Has Right To Assistance" (Law report), The Times, 17 June 1970, p. 8.
- "Council Members". National Alternative Dispute Resolution Advisory Committee. Retrieved 26 April 2010.
- Ansley Ng, "Law Undergrads in Court's Pilot Scheme", Today  (5 January 2007).
-  EWCA Civ 759, available on-line from the website of the British and Irish Legal Information Institute.
- Bowcott, Owen (17 April 2014). "Legal watchdog urges culture shift over fee-charging McKenzie friends". The Guardian. Retrieved 13 September 2015.
- ‘Culture change’ needed to embrace fee-charging McKenzie friends, The Law Society Gazette, Retrieved 15 June 2015
- "Scots judiciary warming to idea of friends in courtroom". The Scotsman. 14 June 2010. Retrieved 13 September 2015.
- Scotland Welcomes McKenzie Friends, Renfrewshire Law Centre, Retrieved 23/06/2015
- Act of Sederunt (Sheriff Court Rules) (Miscellaneous Amendments) (No. 2) 2010