Academic ranks in the United Kingdom

Academic ranks in the United Kingdom are the titles, relative importance and power of employees in universities. In general the country has three academic career pathways: one focused on research one on teaching, and one that combines the two.
Professors.
In the United Kingdom, like most Commonwealth countries (excluding Australia and Canada), as well as in Ireland, traditionally a professor held either an established chair or a personal chair. An established chair is established by the university to meet its needs for academic leadership and standing in a particular area or discipline and the post is filled from a shortlist of applicants; only a suitably qualified person will be appointed. A personal chair is awarded specifically to an individual in recognition of their high levels of achievements and standing in their particular area or discipline. 
In most universities, professorships are reserved for only the most senior academic staff, and other academics are generally known as 'lecturers', 'senior lecturers' and 'readers' (in some Commonwealth countries such as Australia, New Zealand and South Africa, the title 'associate professor' can be used instead of 'reader'). In some countries, senior lecturers are generally paid the same as readers, but the latter title is awarded primarily for research excellence, and traditionally carries higher prestige. Traditionally, heads of departments and other senior academic leadership roles within a university were undertaken by professors.
During the 1990s, however, the University of Oxford introduced Titles of Distinction, enabling their holders to be termed professors or readers while holding academic posts at the level of lecturer. This results in a two-tier professoriate, with statutory professors – or named chairs – having higher status than the relatively recently created category of titular professors. Similar hierarchies among the professoriate exist in a small number of other UK universities. The University of Exeter, University of Reading, University of Warwick, Staffordshire University, Swansea University and Kingston University have adopted the style of 'associate professor' in lieu of 'reader'. The varied practices these changes have brought about have meant that academic ranks in the United Kingdom and in Australia are no longer quite as consistent as they once were.
In the UK the title 'Professor' has historically been reserved for full professors, with lecturers, senior lecturers, and readers generally addressed by their academic qualification (Dr for the holder of a doctorate, Mr/Mrs/Miss/Ms otherwise). However, the current University of Oxford "Style Guide" now notes that Associate Professors ""may, if they wish, use the title of ‘Professor’, or they may keep their previous title of ‘Dr"’. As in the USA, the title of 'professor emeritus' may be awarded to a retired or former professor, who may well retain formal or informal links with the institution where the chair was formerly held.
Named professorships.
Many professorships are named in honour of a distinguished person or after the person who endowed the chair. Some chairs have a long history and considerable prestige attached, such as the , which date back to the 16th century, Regius professorships, or the Lucasian Professor of Mathematics. Some academic societies and professional institution also award or designate certain post holders or members as 'professor' usually being personal awards. The College of Teachers, formerly the College of Preceptors, is a long-standing example of this, as are the amalgamated bodies included in the Society of Teachers in Business Education.
Professors of music.
Somewhat confusingly, instructors at many music conservatoires in the UK are known as professors; for example 'professor of violin'. This designation is quite different from the standard British use of the term and has more in common with the American usage, where the term is applied to any instructor at a college or university. Related to this usage, small-town music teachers, even if they held no degrees, were sometimes called "professors" in years past in the United States.
In the United Kingdom and Ireland the term 'professor' is properly and in formal situations given to singing and instrumental tutors in the music colleges / conservatories of music, usually the older and more august ones: The Royal College of Music, Royal Academy of Music, Trinity College of Music. The expression has become almost obsolete for singing and instrumental tuition in the universities. The same convention applies throughout Europe in the National Colleges of Music.
Pathways.
Research and teaching career pathway.
Academic staff whose responsibilities encompass both research and teaching:
However, it is becoming increasingly common for Russell Group universities to use some form of hybrid terminology: LSE has adopted the American terminology entirely, while UCL has retained the role of Lecturer, but replaced Senior lecturer and Reader with Associate Professor.
Research and teaching career pathway at the University of Oxford.
Specific to the University of Oxford:
Research career pathway.
Academic staff whose main focus is research 
Teaching career pathway.
Academic staff whose main focus is essential teaching, educational needs, and for senior grades, often pedagogic research:
Note that some universities (for example, the University of Glasgow) give the same titles as Research & Teaching track academics to give parity to the roles.
Honorary/visiting ranks.
Common titles for honorary, visiting and honorary visiting academics:
Administrative ranks: England, Wales, and Northern Ireland