Suppose a solicitor in a private firm is appointed as a judge. Are they allowed to continue working as a solicitor in a parallel private capacity? What provisions exist in the way of mitigations to potential conflicts of interest surrounding such a scenario? Tagged england-and-wales and any-jurisdiction, while the question is framed in England-and-Wales-centric terminology. Feel free to answer any adjusted version of the question as may suit your jurisdiction of speciality.
No person holding as a full-time appointment any of the offices listed in Schedule 11 shall—
(a) provide any advocacy or litigation services (in any jurisdiction);
(b) provide any conveyancing or probate services;
(ba) carry on any notarial activities (within the meaning of the Legal Services Act 2007);
(c) practise as a barrister, solicitor, public notary, licensed conveyancer or licensed CLC practitioner, or be indirectly concerned in any such practice;
(d) practise as an advocate or solicitor in Scotland, or be indirectly concerned in any such practice; or
(e) act for any remuneration to himself as an arbitrator or umpire.
The offices listed in Schedule 11 include circuit and district judges, who are those who would sit in a County Court.
This prohibition does not cover retired judges, or part-time ones who receive fees rather than a salary. Fee-paid judges (who hold titles like "deputy district judge" or "recorder") are allowed to continue in private practice, but are subject to conflict-of-interest rules to make sure that they keep those aspects of their lives separate. For example, they are not allowed to promote their private services using their judicial title. These are additional specific safeguards around the general law, where all judges must avoid bias and the appearance of bias. The role also exists in the High Court, and by extension even the Court of Appeal, and can be a stepping-stone to full-time salaried appointment. Such judges only sit for a small number of days each year, and are meant to fill out the full-time bench in order to make specialist expertise available, or just be extra people generally.
While it is commonly understood that salaried judicial office is meant to last until retirement, there is no explicit prohibition on a judge returning to practice, or retiring early in order to do so. It would just be unusual and frowned upon. It is common for retired judges to continue to act in a judicial capacity - as arbitrators, in certain foreign courts, or in their original UK courts if needed - which is different from advocating for or advising a specific client. The terms and conditions of their appointment include the stock language
The Lord Chancellor also regards a judgeship as a lifetime appointment. Any offer of appointment is therefore made on the understanding that appointees will not return to practice.
(quoted in "The shadow of the court: the growing imperative to reform ethical regulation of former judges", Gabrielle Appleby and Alysia Blackham, International & Comparative Law Quarterly 67(3):505-546, July 2018) but this is more in the nature of "we hope you won't" than "we can actually stop you". A former judge who was practicing as a solicitor or barrister would no longer be within the ambit of the judicial misconduct process, but they would be subject to the discipline of the appropriate other regulatory body, so there is still a mechanism in place to govern their professional actions.
Working as a solicitor is incompatible with a judicial appointment
Judges are not prohibited from having outside employment but they must get permission from the CEO of the Justice Department. However, judges wouldn't ask permission to work as a solicitor and the CEO would wonder why this person was a judge if they did.
Part of being a judge is being judicial - having the appearance of detachment, disinterest, impartiality, and, to some extent, remoteness is all part of this. You can't act for just some people and keep up that appearance.
In fact, most judges find the experience to be socially isolating - they have to build a distance between themselves and their former work colleagues and even build a distance into their friendships. Judges are usually quite successful members of society but they can't be seen socialising with politicians, businesspeople, church leaders, or other lawyers because it risks accusations of partisanship. You can't make comments on social media, you can't answer questions like these, you can't express your political or religious opinions, arguably, you can't even barrack for a football team.
Being a judge is more than a full time job
Judges work 60-90 hours per week - when are they going to work another job?